185-205

Question 1

185. What is the difference between a piston and a plunger? SPO 6-7-8

Answer 1

A plunger moves inside stationary rings installed in grooves in the cylinder. A piston has rings installed in grooves in the piston itself.

Question 2

186. Describe a rotary pump and does a rotary pump work on the same principle as a centrifugal pump? SPO 6-7-8 BOW 2-3-4

Answer 2

A positive displacement pump with gears, vanes, screws, lobes, cams, operating in a close fitting casing. They do not use valves in their design, permitting the pump to operate efficiently on both low and high viscosity liquids with a low net positive suction head requirement.
No. The rotary pump is a positive displacement pump

Question 3

187. Give seven advantages to a rotary pump. SPO 6-7-8

Answer 3

1. Self-priming.
2. High suction lifts.
3. High output pressure capable
4. High and low viscosity liquids handled efficiently.
5. High and low head applications handled efficiently.
6. Low N.P.S.H requirements.
7. Wide speed range.

Question 4

188. What are the disadvantages of a rotary pump? What will happen if the discharge valve is closed on a rotary pump? SPO 6-7-8 BOW 34

Answer 4

Slow
Noisy
Prone to wear
Damaged easily

If there is no relief valve, damage to the pump may result.

Question 5

189. Describe how you determine if a centrifugal pump is running. SPO 6-7-8

Answer 5

Check the Delta pressure, discharge pressure, flow switch, differential switch or sight.

Question 6

190. Name two types of centrifugal pumps and describe their differences. SPO 6-7-8 BOW 3-4

Answer 6

In a VOLUTE pump the impeller rotates in a casing of spiral design. The casing is designed to enclose the outer extremity of the impeller. The volute chamber changes velocity head into pressure head.
In a TURBINE pump the impeller is surrounded by diffusion rings which take the place of the spiral casing in the volute pump. The quantity of water depends on the size of the impeller and its speed.

Question 7

191. Make a drawing of a centrifugal pump and explain how it works. (Handout)

Answer 7

The spinning impeller draws liquid into its center and discharges from the outer edge.
Either a volute shaped casing or the diffusion rings direct the liquid toward the discharge, converting velocity energy to pressure head. SPO 9th 420

Question 8

192. Name the parts of a double suction centrifugal pump. SPO 6-7-8

Answer 8

Double inlet impeller, impeller rings, volute casing, casing rings, shaft, shaft sleeves, shaft bearings, grease seals, thrust bearing, bearing end covers, packing, with stuffing boxes or mechanical seals and “O” rings.

Question 9

193. What are the merits of the centrifugal pump? SPO 6-7-8 BOW 2-3-4

Answer 9

Few moving parts, 
Long life
Uniform flow
High capacities
Easy to control
Dependable

Question 10

194. How do you adjust the flow rate of a centrifugal pump? What would happen if the discharge valve was closed on a centrifugal pump? SPO 6-7-8 BOW 2-3-4

Answer 10

By throttling the discharge valve or by changing the speed of the motor. Too much throttling may require the installation of a bypass.
If the valve is closed completely or throttled too much, the pump will slowly overheat.

Question 11

195. What kind of packing is used on centrifugal pumps? Name three advantages of mechanical seals over packing. SPO 6-7-8 LPB 3 BOW 2-3-4

Answer 11

Soft metallic packing.
Longer life, easier to replace, no leakage, less energy used because of less friction, high temperature usage and high pressure usage.

Question 12

196. When operating a pump under 200 degrees F. what kind of seals do you use? Will there be any leakage and why? SPO 6-7-8

Answer 12

Soft metallic packing or mechanical seals.
Mechanical seals should not leak, but with soft packing there will be minimal leakage to cool and lubricate the packing and shaft.

Question 13

197. What problem do you watch for when paralleling two centrifugal pumps? SPO 6-7-8

Answer 13

Make sure the pump capacities remain the same so one pump does not hog the load.

Question 14

198. What would you do if your B.F.W.P. became steam-bound? LPB 2-3

Answer 14

Throttle the discharge a little. Cool the pump with a garden hose or maybe install a city water tap to the suction of the pump. THEN find the cause.

Question 15

199. Is a check valve placed after a pump? Why? SPO 6-7-8 BOW 2-3-4

Answer 15

YES. A check valve relieves the pump of start up pressure and prevents backpressure from injuring the pump by causing it to run backward.

Question 16

200. Define N.P.S.H.

Answer 16

Net Positive Suction Head.

The amount of positive pressure on the inlet of the pump when the pump is on.

Question 17

201. Why is the suction opening on a pump larger than the discharge opening? BOW 3-4

Answer 17

It is to provide a constant volume and capacity to insure a smooth flow.

Question 18

202. Should the supply of water be above or below the pump? Why? Which location will always keep the pump primed? Do you prime a centrifugal pump with it running or with it off? SPO 6-7-8 BOW 3-4

Answer 18

The water supply should be above the pump to keep it primed.

It is primed with the pump off.

Question 19

203. Why is a pump primed? How is a pump primed? SPO 6-7-8

Answer 19

The air must be evacuated suction before water will fill the pump. It cannot pump air.
It can be primed with water from another source.

Question 20

204. Describe how you would align a motor to a pump. SPO 6-7-8

Answer 20

The driver and the driven shaft can be aligned by using a straight edge the length of the coupling halves, a feeler gauge between the coupling halves, a dial indicator or laser alignment.
Always measure the same place as the shafts rotate together.
Proper alignment would be within .005 inch.

Question 21

205. On a pump what is theoretical lift, actual lift, and practical lift? What should you limit your suction lift to? SPO 6-7-8 BOW 3-4

Answer 21

Theoretical 34’
Actual 24’
Practical 14’
10’ to 15’ with cold water. With hot water it is necessary to bring the water to the pump with positive head.