Pressure Control Ppt (Not on written exam)

Question 1

Pressure Controls:

A _______ sensing device used to measure or control the pressure of refrigerant, oil, air, gas, and, water

Answer 1

pressure

Question 2

Pressure Controls: Components of pressure control; Pressure sensing element;

bellows
diaphragm
______ tube

Answer 2

bourden

Question 3

Pressure Controls: Components of pressure control; connecting tube;

capillary tube
braided _____ hose
small diameter tubing (1/4” O.D.)

Electrical switch

Adjustment screws

Answer 3

metallic

Question 4

Pressure Controls:

1. used to switch electrical loads, such as a ________ motor
2. Used to operate devices directly, such as ______

Answer 4

1. compressor

2. valves

Question 5

Pressure Controls: Pressure Control types and switching action;

1. Low pressure control - ____ on a rise in press
2. High pressure control - _____ on a rise in press
3. Low ambient control- ____ on a rise in press
4. oil pressure safety - Normally ____ pressure switch with a time delay circuit and the pressure switch opens on a rise of _________

Answer 5

1. closes
2. opens
3. closes
4. closed, differential

Question 6

Pressure Controls: Operation of pressure controls;

Pressure sensing element moves as a change in pressure is sensed and mechanically opens or closes an ________ switch

1. Switches are ____ acting
2. Can operate over a wide range of ______

Answer 6

electrical

1. snap
2. pressures

Question 7

Pressure Controls: Setting of pressure controls.

1. Control range: the cut in pressure and cut out pressure
2. Cut in: Point at which the control _____ the electrical circuit
3. Cut out: point at which the control _____ the electrical circuit
4. Differential: difference between the cut in and cut out pressure

Answer 7

2. makes

3. opens

Question 8

Low Pressure Control: Application;

1. Used as a safety control to protect against ___ charge
2. Used as temperature control, cycles compressor on _______ refrigerant temperature
3. Used as a _____ down control and shuts down compressor after remote t-stat stops liquid flow

Answer 8

1. low
2. saturated
3. pump down

Question 9

Low pressure control:

1. Operation: Closes on a rise in pressure. _______ and non adjustable types
2. Settings:
   Cut in : adjustment screw
   Differential - cut out = cut in minus differential

Example:
-cut in 35 psig
- diff 5 psig
cutout = 35-5 = 30psig

Answer 9

adjustable

Question 10

Low pressure control: Pump down system;

1. Cut out: close to __ psig without going into vacuum
2. Cut in: Max operating temp, convert to psig (for that refrigerant), divide by two

Answer 10

1. 0

Question 11

Low pressure Control: Example;

Pump down system:

1. HFC 134A system temp range 38F to 40F

Cut-out close to 0psig
Cut-in HFC 134A 40F to Psig
35/2 = 17.5psig

Answer 11

correct example

Question 12

Low Pressure Control: Used as a Temp Control:

Cut - in highest temperature/Pressure from operating range

Answer 12

formula*

Question 13

Low Pressure Control: Used as a Temperature Control:

Cut in/Cut-out calculation:
1. Find coil pressure drop (Pd), take a suction pressure reading as the unit starts

2. Take a second pressure reading as the compressor starts to work when the evaporator comes down to m
3. Substract the difference. The difference will account for pressure drop across the evap
4. Subtract PD from converted low end temp

Answer 13

formula

Question 14

Low Pressure Control:

Note: If the pressure control has a range adjustment or a differential adjustment, the cut-in pressure must be set _____

If pressure control is equipped with a cut -in and a cut-out adjustments, either can be adjusted _____

Answer 14

first

first

Question 15

Low Pressure Control: Example:

HFC 134A system operating range 35F - 40F

1. Cut in 40F = 35Psig
2. Cut out System starts at 35psig and comes down to 25psig, PD= 10
3. 35F to pressure = 30psig - 10psig = 20psig (set point)

Answer 15

exmaple

Question 16

Low Pressure Control:

How to set low pressure controls

1. Install _______ manifold
2. Move the ____ toward the front seat to reduce pressure on the low side of compressor. Check cut-out and watch for cycling of actual pressure
3. ________ as necessary

Answer 16

1. service
2. SSV
3. Re-adjust

Question 17

Quiz:

1. Operating Temperature range: 35F to 38F
   Ref = R22
   Non pump down
   12psig difference

cut in = 38F = 65.7
cut out = 35F to 61.5psig - 12 = 49.5psig

Answer 17

example

Question 18

High Pressure Control:

1. Also called a Pressure limiting _______
2. Used as a safety control to protect the compressor and system when excessive _____ pressure is sensed

Answer 18

1. device

2. high

Question 19

High Pressure control:

Operation;

1. Opens on a ____ in pressure above the set point
2. adjustable and non adjustable types
3. usually _______ reset

Answer 19

1. rise
3. manually

Question 20

High Pressure Control:

Settings:

1. For systems _______ a pressure relief device, the pressure limiting device setting shall not exceed system high-side design pressure.
2. For systems _____ a pressure relief device, the pressure limiting device shall not be set more than 90% of the system high side design pressure

Answer 20

1. without

2. with

Question 21

High Pressure Control: Rule of Thumb;

1. Air cooled condenser systems: ___% below design test pressure
2. Water cooled condenser systems: ___% above normal condensing temp

Answer 21

1. 20%

2. 20%

Question 22

Oil Pressure Safety Control: Operation;

1. Pressure _______ controller
2. Opens on a ______ in net pressure
3. safety control senses suction pressure and oil _____ pressure
4. Time delay to allow compressor to start (90 sec or 120sec)

Answer 22

1. differential
2. decrease
3. pump

Question 23

Oil Pressure Safety Control: Settings;

1. Net oil pressure = oil pump pressure - suction pressure
2. Minimum oil pressure 10psig net oil pressure
3. Normal oil pressure 30-40psig net oil pressure

Answer 23

SETTINGS

Question 24

Oil Pressure Safety Control: Electronic oil pressure control;

Works on pressure differential:

Advantages: More precise timing, no need for capillary connecting tubing on some models, cable connection for pressure sensors, fixed or adjustable settings, usually manual reset

Answer 24

advantages