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28. Low pressure boiler. > Steam System. > Flashcards

Steam System. Flashcards

1
Q
  1. What is dry steam?
A

Steam with moisture content of less than 2% is considered to be saturated steam.

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2
Q
  1. What is boiler trim?
A

Most of the devices connected to a boiler except the burners and their controls are considered boiler trim.

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3
Q
  1. List the various accessories known as boiler trim?
A
  1. Safety relief valves (pop safety).
  2. Water gage (sight glass).
  3. Pressure gage.
  4. Pipe siphon (pigtail).
  5. Pressure trolls.
  6. Low-water cutoff.
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4
Q
  1. Working range on the safety relief valve on a low-pressure steam boiler pops?
A

Opens when the pressure in side the boiler reaches 15 psig and closes when the pressure drops to 12 psig.

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5
Q
  1. Parts of water gage (sight glass)?
A
  1. 2 nipple and coupling connected to boiler.
  2. 2 gage cock.
  3. Sight glass.
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6
Q
  1. How steam gage should be graduated?
A

To at least 1-1/2 times the set pressure of the safety relief valve.

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7
Q
  1. What is compound gage?
A

It measures both positive and negative pressure. On the left side of the gage negative pressure is measured in the range of 0 to 30” of mercury )Hg), on the right side - positive pressure is recorded 0 to 30 psig.

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8
Q
  1. Parts of pipe siphon?
A
  1. Lower handle shutoff cock.
  2. Pig tale.
  3. Toe with inspector test gage connection.
  4. Gage.
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9
Q
  1. Two types of pressure trolls?
A
  1. Additive.

2. Subtructive.

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10
Q
  1. Two types of low-water cutoff?
A
  1. Float type.

2. Electric probe.

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11
Q
  1. What is pressure troll?
A

A mercury switch that turns the burners of the boiler off and on. Controls the operating pressure range of boiler.

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12
Q
  1. What is steam Header?
A

The horizontal piping connected to the boiler steam outlet or outlets.

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13
Q
  1. What is steam supply main?
A

The steam pipe which carried steam from the boiler to the heating units.

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14
Q
  1. What is Hardford loop?
A

Designed to protect boilers against the loss of water under conditions that would otherwise permit water flow out of the boiler into the return main.

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15
Q
  1. What is wet return?
A

Any return line which is located below the water level of the boiler. It is completely full of water and does not contain steam or air.

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16
Q
  1. What is dry return?
A

Any return line located above the boiler water line. A dry return can contain air, steam or condansate.

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17
Q
  1. What is equalizing line (Balance pipe)?
A

A pipe which connects the steam header to the boiler return connection. Drains the condensate from the steam Header and returns it to the boiler below the water line. Equalizes the supply pressure in the return line to boilers. This prevents the boiler water from flowing out of the boiler into the return mail.

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18
Q
  1. What is a drip connection?
A

A vertical pipe that connects the end of steam supply main and the wet return.

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19
Q
  1. What is dimension A?
A

The distance required between the bottom of the last steam cutting line and the boiler water line. Must be used in the gravity return systems in order to overcome the system pressure drop and return the condensate to the boiler.

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20
Q
  1. What is down feed?
A

A steam heating system or part of the system in which the heating units are located below the supply main.

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21
Q
  1. What are heating units?
A

In order to transfer the heat that is in the steam to the space to be heated. heat transfer units are required. Cast iron radiators, convectors and similar heat out put units are used.

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22
Q
  1. What are air vents?
A

Device that allow air to escape when steam begins to circulate. Air vents are heat activated valves that permit air to escape from a steam systems piping and radiators. They close when steam or water enters the vent and reopen when the boiler cycles off, and the temperature inside of the vent drops.

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23
Q
  1. Causes of water hammer in one-pipe system?
A
  1. Water packet or water trap.

2. Condensate produce water hammer.

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24
Q
  1. What is start up (piping and pick-up) load?
A

The condensate that”s formed in bringing the piping and radiators up to steam temperature

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25
Q
  1. What is priming?
A

It is the carrying of small particles of water into the steam piping.

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26
Q
  1. What is foaming?
A

A rapid fluctuation in boiler water level created by impurities on the surface of the water, causing an increase in surface tension of the boiler water.

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27
Q
  1. What does float or air vent contains?
A

A volatile liquid usually a mixture of alcohol and water.

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28
Q
  1. How does steam header and return are connected to boiler?
A

By swing joints.

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29
Q
  1. Why can not You reduce boiler outlet pipe size?
A

This will increase steam velocity that will lead to carry boiler water into steam piping. After that steam will be absorbed into the water causing the steam to condensate before it can reach the heating units.

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30
Q
  1. Why must You use both outlets of steam boiler?
A

If You cap one the steam velocity leaving the boiler will increase and the water will slant towards the uncapped outlet leaving the back section of the boiler exposed to the heat generated by the burner.

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31
Q
  1. What is NOWL?
A

The normal operating water line.

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32
Q
  1. How shall the supply rise into the steam header from boiler?
A

The bottom of the header mast be a minimum 24” above NOWL. That will keep the steam dry, most of the water droplets will fail back into boiler.

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33
Q
  1. How should the steam riser supplying steam to the system main be installed?
A
  1. Shall be after the boiler risers and before the equalizing line . If it will be installed between the boiler risers, the high velocity steam is entering the steam riser from two directions, the drops of water will have no chance to drop down and flow into equalizing line.
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34
Q
  1. How shall equalizing line be connected to boiler?
A

Equalizing line is usually smaller than the header and the elbow at the end of the steam main is pointed straight down.

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35
Q
  1. Location the main air vent/?
A

Near the end of dry return.

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36
Q
  1. What is dimension A for most system?
A

28”.

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37
Q
  1. Operating pressure of most one-pipe system?
A

2 psig.

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38
Q
  1. The operating pressure range of pressure troll for one-pipe system boiler?
A

1-1/2” - 2”.

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39
Q
  1. Two pressure settings for Air vent?
A
  1. Maximum pressure.

2. An operating pressure (drop-off pressure).

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40
Q
  1. Location Main vent?
A
  1. Tee for main vent 15”-18” from the end of the last steam carrying main.
  2. A 6”-10” long pipe nipple should be installed between the top of Tee and the main vent.
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41
Q
  1. How shall the steam supply main be itched away from the boiler?
A

At least 1” for each 20 feet.

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42
Q
  1. Minimum pitch on branch steam piping of one pipe system?
A

1/2” for 10’ of pipe distance.

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43
Q
  1. Two methods of connecting a branch to a steam main?
A
  1. Taken off the main at a 45* angle.

2. Taken off a 90*.

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44
Q
  1. How can You control the flow of steam into radiator of one-pipe system?
A

Radiator valves must be fully open or closet. To regulate the steam flow to radiator You shall regulate the rate at which air is eliminated.

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45
Q
  1. how can You evenly supply heat to all radiators in one-pipe system?
A

Air vents with the largest air venting capacity should be installed on the radiators furthest away. Contact air vent manufactures for air vent selection charts.

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46
Q
  1. What make condensate in gravity return steam system flow back into the boiler?
A

A drip dimension, which is often cooled the “A” - dimension.

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47
Q
  1. What is drip connection?
A

It is just a piece of pipe which is installed vertically at the end of the last steam carrying main.It is standard practice for a system designed for 1/2 psig pressure drop manage the minimum distance for dimension “A” not less than 28” above the boiler water line.

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48
Q
  1. Location Tee for Hartfort loop connection in equalizing line?
A
  1. Residential boiler - 2” below the water line of boiler.

2. 4” for commercial installations.

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49
Q
  1. They shall You use close nipple, when assembling a Hartford loop?
A

If You use longer nipple and the.water level in the boiler drops the nipple will fill with steam and when the condensate does return water hammer will occur.

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50
Q
  1. What is counter flow system?
A

The steam and condensate flow in opposite direction in the steam supply main.

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51
Q
  1. Size of sin steam pipe in a counter flow one-pipe system?
A

It is sized one size larger than other type of one-pipe steam heating system and pitched 1” for each 10’ of pipe distance.

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52
Q
  1. Difference between one- pipe counter flow system and parallel one?
A
  1. The main pitches upward away from the boiler twice as much as a parallel flow system.
  2. No return riser is used, no Hartford loop is needed since since the return is above the water line.
  3. The boiler header must enter the top of the main, unlike parallel flow systems, where the main feeds of the top of the boiler header.
  4. Dimension “A” is at the lowest point of the steam main, but doesn’t have to be 28” because is almost no pressure drop from the boiler to the point of condensate return. The only loss is the friction loss for the condensate.
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53
Q
  1. What is the maximum Header Length for one-pipe counter flow system?
A

100 feet.

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54
Q
  1. Where shall you install main vent for one-pipe parallel system?
A

At the top of each riser and at the end of the steam main.

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55
Q
  1. How shall You pitch down riser connection for one-pipe parallel up feed system?
A

Dripped riser pitch down from the main, I dropped riser connection pitch up ford from the main.

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56
Q
  1. Requirements of one-pipe parallel down feed system?
A

Express steam riser feeds top floor steam main. Steam main feeds steam to down feed risers and branches. Main and dripped risers insensate to returns.

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57
Q
  1. Where shall You provide the Main Vent For one-pipe parallel downfeed system?
A

At the top of each riser and just above the lowest branch on each of the down feed riser.

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58
Q
  1. Riser connection fittings for one-pipe parallel downfeed system Of the main?
A

Tee facing down at 45* engle, 45, 2 90 elbow swing.

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59
Q
  1. What shall You use instead bullhead tee when express riser feed on both sides?
A

Side outlet tee, long radius ell on the top, two 45* ell on the side.

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60
Q
  1. How does Steam Main offset abstractions?
A
  1. Install full size main on the top.
  2. Provide condensate piping below abstraction.
  3. Tee connected two loops together shall be installed with 1” offset following direction of flow.
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61
Q
  1. How shall You install dry return piping around abstraction?
A
  1. Make full size dry return below the abstraction. Provide Tee with clean out on the lowest end of the loop.
  2. Make 1” offset between upstream and downstream tee.
  3. Connect smaller loop above the abstraction for air movement.
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62
Q
  1. The limitation of one-pipe steam system?
A
  1. They are designed to operate at 2 psig.
  2. The normal pressure drop is 1/2 psig per 100’. The length of the steam main is limited to 400’.
  3. Radiator valves must be fully open or closed.
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63
Q
  1. The basic function of steam traps are?
A
  1. Prevent the loss of steam and maintain the pressure differential between the supply and return sides of a steam system.
  2. Allow the passage of condensate, air and other non-condensate gases from the steam supply to the condensate return portion of a steam system.
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64
Q
  1. What is causing corrosion in steam piping and heat transfer units?
A

Carbonic dioxide is liberated from water during the boiling process. If not removed it will be absorbed into the cooled condensate creating carbonic acid.

65
Q
  1. Typical installation drip leg on steam main?
A
  1. Drip leg with valve and cap.
  2. Tee on the drip leg with valve on the side connection for return line condensate line.
  3. Condensate line consist: valve, strainer with valve and discharge pipe, trap.
66
Q
  1. Typical installation of End of the steam main supply?
A
  1. Ell facing down.
  2. Tee with side condensate line and dirt pocket on down connection.
  3. Condensate line include: a) gate valve, b) strainer with damp valve, c) float and thermostatic steam trap with 2 unions, d) test tee with valve, e) gate valve.
67
Q
  1. Tracing line on high temperature product line (above 190 F) return connection?
A
  1. Ell facing down.
  2. Strainer with damp valve.
  3. Thermostatic steam trap.
68
Q
  1. Tracer line where product temperature is below 190 F return connection?
A
  1. Ell facing down.

2. Balanced pressure thermostatic steam trap.

69
Q
  1. Pipe arrangement steam supply to tracing header?
A
  1. Ell on the top of steam main.
  2. Two valve.
  3. Strainer.
  4. Ambient sensing temperature control.
  5. Ell facing down to horizontal header.
  6. On the top of header tracer supply lines connected by valves and unions.
  7. At the end of header facing down outlet for return line.
  8. Return line consist: valve, thermodynamic steam trap with integral strainer, valve and condensate return line.
70
Q
  1. When does steam automatically shut down for tracer line?
A

As ambient temperature rise above product solidification temperature.

71
Q
  1. Piping arrangements for trap draining strainer ahead of PRV?
A
  1. Strainer before PRV has damp line with valve and condensate return line.
  2. Return line has Tee with return line on side and damp valve facing down.
  3. Return line consist valve, check valve, steam trap.
72
Q
  1. Details of the installation of a steam to water convector (heat exchanger). Steam supply?
A
  1. Tee with 1/2” steam bypass.
  2. Gate valve.
  3. Strainer with blowdown valve.
  4. Automatic control valve (stance valve).
  5. Gate valve.
  6. Tee toward bypass connection (bypass line has globe valve).
  7. Pressure gage fitting or adopter.
  8. Reducer as required to main inlet.
73
Q
  1. Details of the installation of a steam to water convector (heat exchanger). Convector tank?
A
  1. 1/2” vacuum breaker connection with 1/2” open end valve.
74
Q
  1. Details of the installation of a steam to water convector (heat exchanger). Return line?
A
  1. Outlet on the end of the tank on its lowest part.
  2. Return line with dirt leg full size of connection.
  3. Tee for trap bypass line controlled by gate valve.
  4. Gate valve.
  5. Strainer.
  6. Gate valve.
  7. F&T trap with two unions.
  8. Check valve.
  9. Gate valve.
  10. Trap bypass tee.
  11. Condensate return piping.
75
Q
  1. Details of the installation of a steam to water convector (heat exchanger). Water line connection?
A

1.Shall allow full length of tube bundle (coil) withdrawal.

76
Q
  1. Details of the installation of a steam to water convector (heat exchanger). Cold water piping?
A
  1. Gate valve.
  2. ASME pressure relief valve.
  3. Thermometer outlet.
  4. Ell with flanged connection to convectors head.
77
Q
  1. Details of the installation of a steam to water convector (heat exchanger). Hot water piping?
A
  1. Convector head outlet with flange (Union).
  2. Flange with tee for temperature sensing element.
  3. Tube removal spool piece with flanges or unions.
  4. Thermometer outlet or fitting.
  5. In line Tangentail Air Release Tank.
  6. Gate valve.
  7. Tangentail air release tank has a) on the top line to expansion tank,
    b) on the bottom drain valve with pipe to drain.
78
Q
  1. Two ways of withdrawal condensate from expansion lookups that are fitted in the vertical plane?
A
  1. Loop below the line - return connection in the bottom of the loop.
  2. Loop above the line - return connection in the front of the loop at the foot of the riser.
  3. Return line consist:
    A) tee on main for condensate outlet,
    B) tee with a drip leg,
    C) thermodynamic steam trap with strainer and two unions, two valves.
79
Q
  1. List the location where steam traps should be installed?
A
  1. At change in elevation of supply and return piping (ahead of risers).
  2. At all low points and at intervals 150’ to 300’ on long horizontal runs.
  3. Ahead of all possible dead-ends of the mains.
  4. For tracing arrangements.
  5. Draining equipment on heat exchangers, kettles, dryers, etc.
  6. Ahead of humidifier, pumps, turbines, etc.
  7. Before or after automatic zone valves, depending on the pitch of the piping.
  8. On all steam to water convector applications and other types of steam heat exchanger installation.
  9. Before expansion joints, bends and loops.
80
Q
  1. Types of steam traps?
A
  1. Thermostatic - operate on the difference in temperature between steam and condensate.
  2. Mechanical - operate on the difference in density of steam and condensate.
  3. Thermodynamic - operate on the difference in thermal energy contained in steam and condensate.
81
Q
  1. How does thermostatic steam trap works?
A

Corrugated metal bellows expands under steam temperature and close the valve.

82
Q
  1. What is bellows filled with?
A

An alcohol, distilled water, an alcohol/water mixture.

83
Q
  1. How can you rebuild balanced pressure steam trap?
A

Replace the thermostatic element or valve seat.

84
Q
  1. How long is cooling leg for balanced pressure steam traps?
A

5’ of in insulated pipe before trap.

85
Q
  1. Use of thermostatic steam trap?
A

They are usually installed on steam radiators.

86
Q
  1. Why are bimetallic thermostatic steam trap better than a corrugated metal bellows?
A

Withstand water hammer, corrosive condensate, superheated steam, high working pressure.

87
Q
  1. What does liquid expansion thermostatic steam trap contain?
A

An oil filled thermostat.

88
Q
  1. One of advantages of liquid expansion thermostatic steam trap?
A

Can be adjusted to discharge condensate at low temperatures, this can reduce steam consumption.

89
Q
  1. What is a float and thermostatic trap?
A

It is combination of a mechanical and thermostatic type steam trap. A float is utilized to eliminate condensate and thermostatic element to discharge air from the trap.

90
Q
  1. Use of float and thermostatic trap?
A
  1. To drip steam mains.
  2. Drip steam supply risers.
  3. For all types of steam heating coils, heat exchanger, etc.
91
Q
  1. Pressure application of a float and thermostatic trap?
A

They are manufactured in both a low and high pressure type.

92
Q
  1. Disadvantage of a float and thermostatic trap?
A
  1. They are susceptible to damage from water hammer.
  2. Because of presence of water inside must be protected from freezing when installed outside.
  3. Can not tolerate corrosive condensate.
  4. Not suitable for use on superheated steam, unless modified.
93
Q
  1. How can you reprise inverted bucket traps?
A

Simply close the valve on the trap’s discharge line for several minutes.

94
Q
  1. Use of float traps?
A

They are often referred to as liquid drainers and are seldom if ever installed on steam system. They may be used to drain water and other liquids from air and gas lines.

95
Q
  1. How does thermodisc steam trap close?
A

After condensate discharge high velocity steam enter the seal disc chamber. This will creat a sudden pressure drop at the lower side of disc and it snaps closed against the seat.

96
Q
  1. The advantages of a piston type impulse trap (thermostatic high pressure steam trap)?
A
  1. Can be used on high pressure and superheated steam systems.
  2. Highly resistant to damage from water hammer, vibration and corrosive condensate.
  3. Will not be damaged by freezing.
97
Q
  1. The dos advantages of a piston type impulse trap?
A
  1. Not suitable for pressure below 3-1/2 psig.
  2. Will cycle rapidly if exposed to low ambient temperatures.
  3. Has a tendency to air bind.
  4. High back-pressure could cause trap failure.
98
Q
  1. Requirements for installation of steam traps?
A
  1. Accessible for repair.
  2. Below the condensate discharge outlets of the equipment.
  3. As close to the equipment as possible except in the case of thermostatic traps which require a cooling leg to be installed ahead of the trap.
99
Q
  1. What kind of fitting require the trap installation?
A
  1. Shutoff valves.
  2. Strainers.
  3. Unions.
  4. Dirt pockets.
  5. Drip legs.
  6. Bypass.
100
Q
  1. Steam trap shutoff valves installation?
A
  1. Before and after steam trap.
  2. If the trap is dripping an individual piece of equipment and there is a shutoff valve on the steam line supplying the unit, the valve before the steam trap is frequently omitted.
  3. If there is a bypass installed around the steam trap , shutoff valves must be installed before and after the trap.
101
Q
  1. Steam trap strainer installation?
A

If trap is not equipped with an internal strainer install a basket strainer ahead of trap.

102
Q
  1. Steam trap strainer cleaning procedure?
A
  1. Close the valve before the strainer.
  2. Open blowoff valve. Pressure inside the trap will drop causing some of the condensate to flash back through the strainer screen, cleaning it.
  3. Slowly reopen the steam supply valve.
103
Q
  1. Steam trap unions installation?
A

Before and after a steam trap at right angles.

104
Q
  1. Steam trap dirt pocket installation?
A

Before steam trap strainer to protect from scale, slag, etc.

105
Q
  1. Steam trap drip legs installation?
A
  1. Up to and including 4” diameter pipe, they should be the same diameter as the steam main.
  2. Above 4” - 1/2 the size of the pipe, but never less than 4” diameter.
106
Q
  1. Steam trap bypass requirements?
A
  1. Only in use if the steam trap fails.

2. If continuous service is called for, install two traps in parallel.

107
Q
  1. When steam trap shall be installed on the runout from a steam supply main to the control valve on a branch line?
A

If it is 10’ or longer, or the pitch back to the supply main is less than 1/2”.

108
Q
  1. How can you elevate condensate?
A
  1. Never elevate condensate under any conditions.
  2. But if it is unavoidable follow this rules:
    A. In low-pressure steam system restrict condensate lift to 1’ per pound of pressure differential.
    B. In high-pressure steam systems should be limited to 2’ of lift per pound of differential.
109
Q
  1. Why must steam traps be tested on a regular basis?
A

1/4” orifice if fail in the open position will cost 1,050 $ per month or 12K $ per year.

110
Q
  1. List three methods which can be used for testing steam traps?
A
  1. Test tee method.
  2. Testing with a listening device.
  3. Temperature meters, infrared thermometers or tempelstiks.
111
Q
  1. What method is the most effective of testing steam traps?
A

Test tee method.

112
Q
  1. How can you test the steam trap by test tee method?
A
  1. Close the valve on the leaving side of the trap and open valve on the test tee.
  2. F&T trap will have continuous flow of condensate.
  3. Invert bucket and thermodynamic steam traps will have an intermittent flow of condensate.
  4. If there is a steady flow of steam that has a blue hue color, it is live steam that is blowing through the trap.
113
Q
  1. When does the test tee method works effectively?
A

On low-pressure systems. On high-pressure systems, where there is a large amount of flash steam, is difficult to determine if it is live steam.

114
Q
  1. How can a two-pipe Gravity system be constructed without installing steam traps?
A

All radiator and end of steam main return lines have to be individually run and tied into the wet return, which is located below the water line of the boiler.

115
Q
  1. Location of the main vent in the two-pipe Gravity return steam heating system?
A

6…8” above and 15…18” from the end of the steam carrying main(s).

116
Q
  1. How can steam flow into the heating unit be controlled in two-pipe Gravity return steam heating system?
A

A thermostatically controlled radiator valve will open or close automatically in response to room air temperature.

117
Q
  1. Life expectancy of thermostatic radiator traps and F&T steam traps?
A
  1. Thermostatic steam traps - 3…5 years.

2. F&T traps - 5…7 years.

118
Q
  1. How does trap failure affect steam heating system operation?
A

If enough traps fail in the open position, the steam would Dow into the condensate return line pressurizing it and also restricting circulation. In order to have circulation the steam pressure in the supply main must be greater than the pressure in the condensate return line.

119
Q
  1. What is the major drawback of a two-pipe Gravity system?
A

It is getting the returning condensate back into the boiler.

120
Q
  1. What is used to return water to the boiler in a two-pipe Gravity return system?
A

“A” dimension (drip leg) 60” long (28”x2 psig 4” for friction loss). When the steam traps cycle close there is no left over steam pressure to help push the condensate back into the boiler.

121
Q
  1. When should a mechanical means of returning water to a boiler on two-pipe steam system be used?
A
  1. When replanting a steam boiler.
  2. When modifying an existing steam system.
  3. If the proper amount of headroom needed to return water to the boiler by Gravity.
  4. If the condensate is slow returning to the boiler and there is a possibility that a low water condition could occur.
122
Q
  1. What is the difference between the Gravity and mechanical return system?
A
  1. The end of the main vent is not needed in mechanical return system. Air exit system by means of the condensate receiver open vent line.
  2. There is no Hartford loop when the pump discharge is close to the boiler.
123
Q
  1. How should the line entering condensate receiver be equipped?
A

With a shutoff valve and strainer.

124
Q
  1. What is the purpose of installing a strainer, a check valve, a pressure gage and a plug valve on condensate receiver?
A
  1. The strainer protect the pump impeller from dirt, slag, etc.
  2. Check valve prevent back flow.
  3. Plug valve regulate the pump discharge pressure.
  4. Pressure gage read pump discharge pressure.
125
Q
  1. Pressure application of two-pipe steam system with mechanical return?
A
  1. The maximum pressure generated by low-pressure steam boiler is 15 psig.
  2. Additional pressure needed to overcome resistance in the pipping is 5 psig.
  3. If condensate is pumped into the boiler at 20 psig the water will scream through the short run of pipe, creating turbulence in the boiler and cause the check valve to chatter.
  4. The plug valve would be partially closed, so the pumps discharge pressure entering the boiler is 7 psig.
  5. The operating pressure is 2 psig and the additional pressure needed to overcome resistance in the piping would be 5 psig.
126
Q
  1. Why are boiler feed pumps usually installed?
A

To supply water to large steam boilers, fire tube boilers or system that have a time lag problem.

127
Q
  1. Boiler feedpump installation?
A
  1. condensate return piping.
  2. Make up water tank.
  3. Cold water supply line to make up water feeder.
  4. Low-water cutoff.
  5. Boiler feed pump.
  6. Boiler feed piping.
128
Q
  1. What are the major differences between a boiler feed pump and a condensate receiver?
A
  1. The pump motor on a boiler feed pump is started by a low water condition in a boiler. A high water level in the condensate receiver starts the pump motor on a condensate receiver.
  2. The receiver on a boiler feed pump is sized to insure that there is enough water to supply water to the boiler. It is equipped with a water feeder to maintain water level. The receiver is also sized to accommodate the slow returning condensate and the water added by water feeder without flooding the boiler. A condensate receiver is small and does not hold very much water.
129
Q
  1. How is a boiler feed pump receiver sized?
A

To provide for 30 minutes of boiler steaming time.

130
Q
  1. How can you find a boiler evaporative capacity?
A 
C=O/(LhxMxT), where 
C - boiler evaporative capacity in gallons per minute, 
O - boiler gross output in Btu/hr, 
Lh - latent heat of evaporation in Btu,
M - mass weight in lb/gal,
T - minutes per hour.
131
Q
  1. How should the boiler feed pump be sized?
A

To supply twice the amount of water vaporized in gallons per minute.

132
Q
  1. What is the maximum boiler feed pump capacity?
A

It should be no more than 1-1/2 times the pump size calculated.

133
Q
  1. The problems that could create by a boiler feed pump with too much capacity?
A
  1. Sediment that is in the boiler could be stirred up, this would have an adverse effect on boiler operation.
  2. It is possible that the feed pump could overfill a boiler before the water level controller could react to the elevated water line.
  3. Water hummer, thermal shock and short cycling are conditions which could occur.
134
Q
  1. How is the receiver tank sized?
A
  1. Only 75% of its capacity can be used as storage for the boiler. Storage factor 100/75= 1.33.
  2. Ts=CxFxBsT, where
    Ts - tank size in gallons,
    C - boiler evaporative capacity in gpm,
    F - storage factor,
    BsT - boiler steaming time.
135
Q
  1. What is meant by the term “time lag”?
A

It is the amount of time required for condensate to begin returning to the boiler once the boiler has begun steaming.

136
Q
  1. When a new boiler with smaller water content is installed, condensate is slow returning to the boiler. How can an installation of this type cause a potential problem?
A
  1. When the water level drops, the low-water cutoff will shut the boiler off.
  2. If the boiler is equipped with a make up water feeder, in the event of low water condition, make up water will be fed into the boiler. When the condensate finally returns there will be excessive water in the boiler. This reduces the room needed to create steam and the excess water would have to be drained from the boiler.
137
Q
  1. How can a time lag problem be solved?
A
  1. For small residential boiler install an external reservoir pipe.
  2. Install condensate tank and pump.
  3. Install a boiler feed pump.
  4. Install a prob type low-water cutoff.
138
Q
  1. Condensate receiver will not react to a low water condition in the boiler. How can you prevent this a time log problem?
A
  1. The receiver must be supplied with make-up water using an electric solenoid or an electric motor-operated valve. This valve is controlled by a float switch in the receiver to maintain the proper level of make-up water.
  2. Condensate requires pumps wired so they will be activated by a low water condition in a boiler.
139
Q
  1. Two types of Paul systems?
A
  1. One-pipe Paul system.

2. Two-pipe Paul system.

140
Q
  1. Describe the operation of a Paul system?
A

Tubing is attached to the discharge of the air vent. It is run back and connected to a vacuum pump or an injector.

141
Q
  1. How does the injector of steam system create a vacuum?
A

By high pressure steam, air or water passing through It.

142
Q
  1. How can space temperature be controlled in heating system with a vacuum pump?
A

Since steam is being supplied and condensate leaves the heating units through separate lines, temperature can be controlled by a manual or thermostatically controlled radiator valves.

143
Q
  1. What are some problems associated with vacuum steam heating system?
A

Vacuum pump are designed to pump water, not steam. The live steam will destroy the vacuum pump. When steam traps fail live steam will blow through the trap and enter the return line.

144
Q
  1. Three attempted fixes for buildings with broken vacuum pumps?
A
  1. Convert the vacuum system to mechanical return system, by installing a boiler feed pump.
  2. Open the drains on the return piping and let the condensate drain out of the system.
  3. Install a manifold consisting of several steam traps or one large trap before vacuum pump.
145
Q
  1. Why converting vacuum system to a mechanical return system does not work?
A

The pipe sizes on a vacuum system are one size smaller then they would be in a mechanical return. It would cause uneven or no heat in the heat transfer units and slower venting or condensate return.

146
Q
  1. Why opening the drain on the return piping of vacuum system can not be used in leu of fixing vacuum pump?
A

The raw make-up water contains oxygen, which over time will cause the boiler and return. piping to fail. Make-up water could also have a high mineral content. Minerals deposits could cause boiler or boiler control failure.

147
Q
  1. Why can not you install trap before the vacuum pump in leu of fixing fault steam traps?
A

When the steam trap close the vacuum stops at the trap, air, condensate and steam circulation is slowed and steam distribution is uneven or nonexistent. Also condensate can flash to steam as it passes through the trap. If enough flash steam enter the vacuum pump will fail.

148
Q
  1. Parts of typical two-pipe vacuum system?
A
  1. Vacuum switch.
  2. Control line.
  3. Vacuum breaker.
  4. Equalizing line.
  5. Lift fitting.
149
Q
  1. Describe the function of vacuum switch of two-pipe vacuum system?
A

It senses the pressure at the end of the vacuum return main. it cycles the pump on at 3 and shutoff when the vacuum is pulled down to 8” of mercury thus maintaining a pressure of about 5 1/2” of mercury in return main.

150
Q
  1. What is control line in vacuum two-pipe steam heating system?
A

The pipe that connects the vacuum switch to the end of return main.

151
Q
  1. What is the function of the vacuum breaker in two-pipe steam heating system?
A

It protect the vacuum pump from creating too low a vacuum. The pump will be adversely affected if the induced vacuum that pump creates is too low. The vacuum breaker will open and let air into the system when the pressure inside the pump drop to 15” of mercury.

152
Q
  1. Why does an equalizing line is installed in two-pipe vacuum heating system?
A

Condensing of steam in the steam supply side of the system, when the boiler cycles off can create a deep vacuum. This vacuum can be lower than the vacuum on the return side of the system. This could restrict the flow of condensate back to the vacuum pump and curtail steam flow, when the system cycles on. The equalizing line eliminate vacuum by taking off the overflow pipe of the vacuum pump.

153
Q
  1. How does an equalizing line work in two-pipe steam heating system?
A
  1. The check valve in the vent line prevents the loss of vacuum while the system is in operation.
  2. The check valve in the equalizing line remains closed as long as the pressure in the supply side is higher than return side pressure. If the pressure on the supply drops lower than the pressure in the return side piping, check valve will open equalizing system pressure.
154
Q
  1. What is installed to elevate condensate in a vacuum steam heating system?
A
  1. Condensate receiver with the vent tied into the vacuum return line.
  2. In an effort to save money lift fitting can be incorporated into many system designs.
155
Q
  1. Why should lift fitting be avoided?
A
  1. When installed the vacuum pump must be run continuously.
  2. Vacuum pumps might have to produce a vacuum that is higher than regular system operating pressure to elevate the condensate.
  3. Condensate might flash when subject to lower return pressure. This could result an objectionable noise and vacuum pump damage.
156
Q
  1. How is lift achieved by lift fitting in vacuum two-pipe steam heating system?
A

Water seal separates the supply and return side of system. The vacuum pump reduces the pressure on the outlet of the lift fitting. A slug of water will be discard out of the fitting into the return line. The lift of condensate from the outlet of the fitting is limited to 5 feet.

157
Q
  1. What shall you do If additional lift is required in vacuum return line of steam heating system?
A

A second lift fitting can be installed. The total lift that can be added using two fittings is limited to 8’.

158
Q
  1. Describe the cycle of operation of a jet type vacuum pump for combination, where the lower compartment is receiver?
A
  1. The vacuum pressure in the system falls below the vacuum pump’s switch on setting, or condensate level in receiver is high enough so float switch start centrifugal pump.
  2. The centrifugal pump circulates the water in the bottom of the upper tame through an ejectors when an increase in water velocity is realized a corresponding pressure drops occurs. That opens check valve and let water, air, any non-condensate gases flow from the lower tank (receiver) into the upper tank. Air that has been carried along or entrained with the condensate flowing from the lower to the upper tank is liberated from the system and flows out through opening in upper tank.
  3. When the condensate level in the upper tank rises, the float will open pilot valve and the condensate, instead of being pumped through the vacuum jets is pumped into the boiler.
159
Q
  1. Why are positive displacement vacuum pump seldomely installed in vacuum return steam heating systems?
A

The have poor air removal capacity and the close tolerances between the pumps internal parts leads to extensive maintenance.

28. Low pressure boiler. (5 decks)

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