Question for those of you who might have a couple years experience pump testing.
We're trying to interpret a couple things written into a document that essentially parallels the NFPA 1911 code. We have an environment where we are unable to draft for the tests and realize that we can use hydrants to supply the long term water.
The clause I'm not 100% on states words to the effect "If the intake pressure gauge reads 30psi and the test requires a net pump pressure of 150psi, the discharge test gauge should read 180psi." This is given as an example of "net discharge pressure."
I am having a real hard time getting my head around this. Fundamentally, at least to my current understanding (and correct me if I'm wrong, please!), it's not in fact the compound pressure that's giving me the figure I need would need to add- but instead the DIFFERENCE in the compound pressure between when I wasn't flowing and when I started flowing.
As I see it, if the compound / residual pressure before I started flowing was 50, and after I started flowing it dropped to 35, then the amount the hydrant is actually contributing to my discharge flow / pressure is only 15psi. The 35 is the flow I could tap into later... which we're not testing. So to me that's a useless figure (except for safety).
So would I in fact want to keep running the pump at 150psi+15psi? Or actually run it at 150psi+35psi?
Thanks in advance
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09-15-2009, 01:12 AM #1
Pump Testing National Fire Code translationIan "Eno" McLeod
09-15-2009, 01:31 AM #2
- Join Date
- May 2001
- Greensboro, NC USA
If I understand your question correctly..... run it at 150 + 35.
Here's my explanation.
Pumps are typically rated at X amount of flow at Y amount of NET DISCHARGE PRESSURE (NDP). NDP is the amount of pressure added to the water by the pump.
To find NDP, simply calculate the difference between intake pressure and discharge pressure, or back calculate if there is a specific NDP you're looking for.
Example: Intake at 30 psi, Discharge at 180.
NDP = DP - IP
NDP = 180 - 30
NDP = 150
Another: Intake = 23.5" Hg (10 psi of vacuum), Discharge at 140
NDP = DP - IP
NDP = 140psi - (-23.5 Hg) convert to like units...
23.5 x 0.434 = 10
NDP = 140 - (-10)
NDP = 150
You should have an copy of the original test of the pump, possibly performed/observed by Underwriters Laboratories. If should give detailed measurements of the pump speed when it's flowing the intended amount & pressure of water. If you get your pump set up and it the pump speed doesn't resemble the original test, then something is wrong.
Last edited by txgp17; 10-09-2009 at 08:30 PM.The American people will never knowingly adopt Socialism. But under the name of 'liberalism' they will adopt every fragment of the Socialist program, until one day America will be a Socialist nation, without knowing how it happened. --Norman Mattoon Thomas, 6 time presidential candidate for the Socialist Party of America
09-15-2009, 04:23 AM #3
Thanks TX... looks like the part I'd neglected was that the residual pressure is actually being applied to the water in the pump (and not the pump itself)... and therefore can be added in your NDP equation.
And- if that's wrong... well... THAT actually makes sense to me so may ignorance be my professor!
I wasn't aware that NDP had a formula... but if I'd known that I'd have not tried to rationalize it another way.
I thank you again!Ian "Eno" McLeod
09-16-2009, 09:24 AM #4
Pump the rig at its rated pump pressure for capacity 150
The water coming in from the plug will natually add in the pressure leaving the pump. No need to add the static pressure to you PDP.
The best and only real way to test the 100% 70% 50% rated pump test is at draft. That way the pump is doing all the work and gets no help from a static water supply. Of course I think you already knew this. Just pointing it out for those who may not know.
10-09-2009, 03:26 AM #5
Yeah- the problem we have is that we have no drafting site. Another challenge is in finding enough nozzles to sustain 3500gpm (our rated pump capacity)
It also doesn't help that we have a water system that is capable of generating 35psi residual while flowing over 6000gpm out of a single hydrant. Needless to say it's all well and good to be able to add 30psi here and there... a bit harder to start having to add 150psi at a meagre output of 3500gpm!
Anyone else out there commonly do their own pump tests? I'm wondering- if the techs who fix the pump (when required) need to run the test again anyways to dial it in... shouldn't they just do it in the first place?
Thanks!Ian "Eno" McLeod
10-09-2009, 09:44 AM #6
- Join Date
- Aug 2005
We test our own and except for the pump itself we do our own maintenance and repair. We either use a draft pit or on smaller pumps we use a large dump tank. But we do not have anything that is 3500GPM. In fact you could add our two engines and one of our tankers together and not have 3500 GPM. What kind of engine is this? I am assuming a two stage pump?
10-10-2009, 03:04 AM #7
It's an 8FG in a pierce... industrial jobby. Deck howitzer on the roof capable of 5000gpm or so (Renegade). Pretty big (huge) but not as big as the Williams trailer with the 6000gpm on board... Still haven't figured out how we're going to do that one. Still just a single stage, both of them.Ian "Eno" McLeod
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