Diesel pump control 1

[Weldinspect]

Hello, how is a Diesel engine fire pump supposed to be controlled?

In a test we did yesterday when it reached the top pressure it stoped and inmediatelly when reaching the low set it started again when we were only using 4 hoses. If we use 5 water lines this didn´t happen, the pump is a 300 gpm model and the 4 hoses would only take 158 gpm.

Also the relief valve is a 1/4" diameter, it seems to me to be to small?

Should the relief valve help with the control or is it only for safety?

 

[LCREP]

A few questions

1. What are the pressure settings on the pump? What psi does the pump come on and go off at.

2. Does the pump have a shut down timer, if so what is timer set to shut off, many are set for shut down 7 minutes of pump operation is very common time.

3. What was the suction pressure when the pump was flowing 158gpm?

4. Was the relief valve on the pump or was it down stream from the pump. Does the pump have a casing relief valve?

5. What is the pump rating psi and GPM. Is it connected to a city supply or a tank?

 

[Weldinspect]

Thanks LCREP this is the data:

1. On: 142 psi, Off: 170 psi
2. No timer at all. Are they allowed by NFPA 20?
3.No data on this only the pump pressure at the manifold: 165 psi
4.Downstream, no relief valve on pump
5. 300 gpm, connected to a tank

 

[LCREP]

Who is the mfg of the controller and model number?

 

[Weldinspect]

The control system is just conformed by pressure switches with high and low settings, the pump system is not made in the US but the catalog says it is NFPA 20

 

[stookeyfpe]

The pump is driven by the hydraulic demand based on the original design. Your pump design is odd. Your flow is very low but the pressure demands are very high. Your hose flow values are also odd because where I work, we commonly flow 250 GPM through 2.5 inch hoses during standpipe tests.

Was this an annual or acceptance test?
What is the fire pump supplying?

This sounds like a fire pump supplying a Class II standpipe system for small hose streams. Again, not enough information.

 

[LCREP]

Some things to check

1.Is the valve from the tank to the pump suction open 100%.
2. If the valve is open when was the last time the inside of the tank was inspected. Can the suction pipe be blocked? Does the pipe have a anti vortex plate installed?
3. Was the tank filled before the test, how much water was in the tank after the test. How much does the tank hold.
4. On the discharge side of the pump are the valves open 100%? If open check the interior of the pipe for restriction plates. They will cut down on the flow, I have run into this a few times trying to keep the psi high.
5. How does this test compare to past tests, is this a new problem, or has always been this way.
6. Are the pressure switches OK, perhaps replace them.

 

[chicopee]

Read your NFPA 20 on centrifugal pumps, controls and the pump characteristic curve in the appendix. It seems that the motor shuts down at or slightly above the pump churn point which coincidentally is close to the manifold working pressure of 165 psig. Since you know the churn pressure and you can test the pump at overflow condition,ie. is without discharge attachments, you can estimate the pump rated pressure and flow rate using the characteristic pump curve percentage values in the appendix; obviously you'll need to take into consideration the conditions on the supply side of the pump. At least you'll have something, may be not totally accurate, to go on.
You have not stated the size and length of the hoses when you did your test, so that info. along with motor HP and inlet and outlet sizes of the pump would help a little bit to the above responders.

 

[Weldinspect]

stookeyfpe

Was this an annual or acceptance test? Acceptance
What is the fire pump supplying? A hangar (yes I know 1 1/2" hoses are not allowed)

LCREP


1.Is the valve from the tank to the pump suction open 100%. YES

2. If the valve is open when was the last time the inside of the tank was inspected. Can the suction pipe be blocked? Does the pipe have a anti vortex plate installed? THE TANKS WAS INSPECTED JUST A COPULE OF MONTHS AGO WHEN THE PROJECT WAS A T IT´S FINAL STAGE

3. Was the tank filled before the test, how much water was in the tank after the test. How much does the tank hold. THE TANK WAS FULL AND HAS AN AUTOMATIC FILLING SYSTEM, WE DIDN´T CHEK AT THE END. TOTAL VOLUME FOR HAL AN HOUR

4. On the discharge side of the pump are the valves open 100%? If open check the interior of the pipe for restriction plates. They will cut down on the flow, I have run into this a few times trying to keep the psi high. FULLY OPEN, RESTRICTION PLATES ARE NOT SUPPOSED TO BE THERE BUY I WILL CHECK

5. How does this test compare to past tests, is this a new problem, or has always been this way. THIS WAS AN ACEPTANCE TEST

6. Are the pressure switches OK, perhaps replace them. THEY ARE NEW AND WORK AS EXPECTED

Chicopee

I didn´t read the appendix recently thanks

NOTE: NFPA 20 section/ 4.18.2.2 If the relief valve is not sized hydraulically, the relief
valve size shall not be less than that given in Section 4.26. AND FOR A 300 GPM PUMP IT STATES THE RELIEF VALVE TO BE 2 1/2" NOT 1/2" AS WE HAVE. SO I BELIEVE THIS VALVE IS TOO SMALL TO TAKE THE ECCES FLOW?

 

[Weldinspect]

Please let´s concentrate in the main question:

...how is a Diesel engine fire pump supposed to be controlled?

a. High/low pressure switch?
b. Same as before plus an adecuate relief valve?
c. other? (RPM engine control, etc.)

 

[LCREP]

As I see it you have few problems

1. The pump is rated for 300 GPM, as per NFPA 20 and 25 you should have flowed 150% or 450 GPM at 65% of the rated pressure. Perhaps the pipes are too small on the suction and discharge and do not meet the minimum set by NFPA 20, assuming NFPA was used as the installation standard. Maybe something is stuck in the pump impeller.

2. The relief valve should only open if the pump pressure is greater than what the system components are rated for. This can happen with a diesel pump in an overspeed condition. Yes you should have a properly sized valve, but this is not the reason the pump stopped, or did not reach the required flow and pressure.

3. If the pump shut down that can be a few things, an over speed condition on the engine, you do have a timer in the pump controller and it shut the pump down after so many mins, or a bad pressure switch, or the pressure is not set properly.


What is the pump rating including the rpm, psi at 300 GPM?

What was the suction and discharge pressures at each flow and non flowing condition, rpm and GPM?

Perhaps the engine is not operating at the rated rpm, thus reducing psi and GPM.

 

[Weldinspect]

1- I Will have to check all diameters and no, NFPA is not contractual but the pump`s catalog says it is
2- The only control this systema has is the pressure switch, what else can stop it?
3- There is no timer, we will have to check the p. s. setting

P = 148 psi
HP = 80 John Deere
RPM = 2400

What was the suction and discharge pressures at each flow and non flowing condition, rpm and GPM? The RPM reached 2600 RPM so as you say it could have been an overspeed condition; we could not measure the flow at this time

 

[LCREP]

The pressure setting maybe too low. Do you have a placard on the pump with the pump details? I am only know NFPA 20, so if the pump is not designed to meet 20 what I say below may not apply.

If the pump is rated 148 psi @ 300gpm then the following would give you some ball park numbers.

148 psi times 1.20 gives you a churn pressure of 177 psi. NFPA 20 says the pump can churn from 100-140% of the rating. Many pumps are in the 120% range that is how I got 177 psi. To know for sure look at the placard on the pump it will say shut off psi .

At 450 GPM the pump should produce 96 psi this is based on 148 psi times .65

So the pump would be rated as follows.

Churn 177 psi @ 0 GPM
148 psi @ 300 GPM
96 psi @ 450 GPM.

Based on this the pressures should be adjusted IF I have the correct info, it all starts with the placard pump data.

 

[Weldinspect]

I am sorry I didn´t send the plate data before, please find it attached. Here the 450% flow pressure is 137 psi. Sorry I said before the shut off pressure was 170 psi, after watching a video I clearly saw it is 150 psi.

 

[LCREP]

Basic question when the test was conducted was calibrate gauges used, or did they use the gauges on the pump. Perhaps you have bad gauge reading.

The pump placard psi and GPM does not meet NFPA 20, not sure I can provide more help.

If you are on LinkedIn they have a pump forum for out of the USA, perhaps try them.

 

[Weldinspect]

The contractor did not show the calibration certificates. Thank you LCREP I will search for the Linkedin forum and well I guess we have more work to do...

How do you know that the pumo does not acomplish NFPA 20?