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Pressure or Volume

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  • Pressure or Volume

    For those of you running two stage pumps, do you leave your transfer valve set in the pressure or volume setting? Just curious as to why you use this particular setting; tradition, manufacturer's recommendation, department SOP or what? In my department we always left the pumps in pressure until we started pumping more than half the capacity of the pump, at which time we switched over to volume. This was done of course to cause the least amount of strain on the engine. Recently, we have eliminated small booster lines which required high pressures (our smallest lines are 1 3/4") and we use LDH to supply engines or master streams (no more duel 2 1/2"s}. We do not pump more than 200 PSI through the LDH. Because of this I have started leaving my engine in the volume position. I just like the idea of having maximum flow capacity immediately available without having to worry about switching over. Is my thinking flawed or does anyone else do this?

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    Mike Gentili, Capt.
    New Bedford Fire Dept.

  • #2
    Waterous Company recommends that you use it in the pressure mode until more than 50% of the rated capacity is required. Which is how you ran it before. It is true that the pump is more efficient in pressure for the low flow/high pressure operation. 99% of the time we only use a 1 1-3/4" line off of the apparatus. Running the pump in series will create less heat and less re-circulation cavitation (when the pump is trying to pump more volume than you are taking off of the discharge side). Most fires you know when you need more than 50% of the rated capacity. Switching it also exercises the transfer valve and flushes any sand that may have accumulated in the housing.

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    • #3
      We house our squrts in the pressure mode. At the time we arrive we will be instructed on whether our squrt will be deployed. if so then the pump will be moved over into the volume stage. you get a more efficient pump by doing the 50% flow rule. keep this in mind and you will have a long lasting more efficiently performing pump.

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      Captain James Collier
      McMahan Fire Rescue
      KCTCS Area 6 Instructor

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      • #4
        Thanks for the replies guys. I was always taught the same things you are saying about the 50% rule and I fully agree with this when we needed higher pressures. The reason I have changed my position now is the fact that we almost always pump between 100 and 200 psi now no matter what lines are flowing. We have an excellent water supply system with closely spaced hydrants and pressures in the 90-100 psi range in most areas of the city. This good hydrant pressure makes our net pump pressure fairly low. We can easily maintain the necessary pressures in volume and keep the engine RPMs around 1500-2500 with no unnecessary overheating. I have more often than not seen our engines straining to feed master streams or multiple lines because the pump operator failed to change over to volume. In actuality, we really only need single stage pumps and all our new engines are being ordered that way.

        As far as exercising the transfer valve, we do that as part of our weekly apparatus maintenance program. We operate the pumps, transfer valve, priming pump, and relief valve every Saturday.

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        • #5
          Our single two stage pump (is that proper grammar?) is kept in volume all the time.

          Reason is it is on the ladder, and would be a rare event for the truck to have to pump one of it's handlines -- almost always it's being run to feed the stick.

          Of course in a few more weeks the new ladder will be in with it's single stage and our days of two stage pumps will end

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          • #6
            I agree with most of what I've read here. If you pump over 1/2 the capacity of the pump, pump in volume. We keep our pumpers with the pumps in VOLUME, and when we start water, if it's just a handline or two we switch to pressure. This helps exercise the transfer valve. It is an SOP in our dept. and we train, train, train that way so we "generally" don't forget.

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            • #7
              One thing to remember on the changeover valve is that you can do a safe and quick switch when your intake pressure is within 50 psi of your discharge. i have done this many times on our squrt during exercises. I will have handlines off for the drill and command will call for the squrt to deploy. I will go ahead and do my switch before i even take the stick out of the bed. This way i can continue my ops and my interior crews can as well until i need to switch over to the master stream. Then when they back out, we can have the lines for outside use as well as the sticks in the air.

              ------------------
              Captain James Collier
              McMahan Fire Rescue
              KCTCS Area 6 Instructor

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