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Does high discharge pressures hurt the engine/pump?
One characteristic that always gets brought up in low pressure hose(low fricition loss characteristics)and low pressure nozzle discussions is the fact that they save wear and tear on the apparatus engine and pump. I don't think this is an issue. Any thoughts?
Replies to This Discussion
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Permalink Reply by Ben Waller on
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That's not a valid comparison. The tach reading at 50 MPH isn't pertinent to pumping.
The valid comparison is the tach reading when pumping at a lower pressure than the increased tach reading when pumping at a higher pressure with the same hose layout and nozzle pressure.
Higher RPMs in the engine and pump while pumping do increase wear and lead to increased maintanance frequency and cost.
No one here that doesn't fight fire in Vegas has to worry about pumping that scenario, which is an extreme outlier, not the norm.
Once again, pumping with 50 PSI nozzles puts less wear on the pump and the engine than does pumping exactly the same hose layout with a 100 PSI nozzle.
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Permalink Reply by FETC on
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300 psi. DP - Isn't that exceeding the hose testing requirements? Are they using special high pressure supply line?
I understand the theory of RPM via over the road travel speeds, but when we repetitively open and close nozzles, gates and appliances during the movement of water, then PSI does cause greater wear on the pump over time as compared to lower PSI layouts.
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Permalink Reply by Don Catenacci on
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Heck, my career FD hose tests to 400 psi. So 300 would be cool with us.
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I gotta ask, are you doing 400 psi on a hose tester or are you using the engine?
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Tested with a hose tester.
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Permalink Reply by Paul Shapiro on
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Ben, engine RPM is the same wether the engine is driving the apparatus or the pump.
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You're still missing the point.
What the engine does when it is driving is not pertinent to a discussion about pumping...unless you're also arguing that we need to drive more slowly on calls to reduce that wear, too.
What matters to a pumping wear discussion is the engine RPM when pumping at a lower pressure vs. the engine RPM when pumping at a higher pressure.
Since it requires more throttle to pump at the higher pressure, pumping at the higher pressure increases wear in comparison to pumping at lower pressures.
More RPM equals more friction equals more wear.
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Unless your hose manufacturer says something different, 400 PSI is too high, even for annual service tests.
The NFPA uses 300 PSI as the standard and ISO says 250 PSI for hose of 3-inch diameter and smaller. Here's a quick reference for both.
One of the reasons is that very high hose test pressures are a safety problem for the firefighters doing the test.
The PSI standard is the same regardless of whether you test the hose with a fire pump or with a hose tester.
That said, current standards call for hose testing to be done in a specific manner, using a hose tester.
Our apparatus is specifically prohibited from being used to test hose by the manufacturer.
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Permalink Reply by Paul Spencer on
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Ben, I would really like to better understand this. Exactly what component or part is wearing inside the pump?
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In fact while pumping the Allison transmission is in what we call fourth gear lock up which makes the 50 mph statement accurate. Older engines would show the speedo spinning. Old school engines if the pump panel throttle broke you could jump in the cab and run the pump with the accelerator pedal and speedometer. Most pumping operations never get up to highway speeds.
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OK Ben let me try to constructivly disagree with yo on the hose pressure ratings put out there by NFPA and ISO. First NFPA. The documents you posted said per NFPA hose shall be tested at a MINIMUM of 300 psi. Again I say minimum. It does not say that hose can be tested higher. Most
1-1/2", 1-3/4", 2" 2-1/2", and 3" hose manufactured today rates there hose at a 1200 psi BURST pressure, a 400 psi Service pressure, and a operating pressure of 10% less then the annual service pressure which is 365 psi if you test it at 400 psi.LDH SUPPLY HOSE according to NFPA and the manufacturers states tha a 200 psi test. pressure be used. This doesn't mean that you have to test the hose at 400 psi but it is rated for it and is allowed by NFPA and more importantly the manufacturers.
I read the note about ISOs rating of 300 and I don't agree with it and it is my understanding, correct me if I am wrong , that ISO doesn't set these kind of standards for FD and hose manufacturers, NFPA does.
As far as testing the hose I think a two stage pump can reach 400 psi. Two single stage pumps can deffinately reach 400 psi and a hose tester can as well.
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For some reason my last post was cut in have and I also did not get a chance to edit it. First I noted a mistake I made. I said that NFPA states that you cannot test hose higher than 300 psi. I meant to say that NFPA allows you to test hose higher than 300 psi and the manufacturers do as well. They state that the 300 psi is a minimum. Also NFPA states that pumps and the discharge and inke plumbing systems and valves be hydrostatically tested at a minimum of 500 psi. Again the minimum word. My department requires a 600 psi PDP and got the ok from Waterous to do so.
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