Two Stage Pump Questions

[CMM310]

I recently became involved with a volunteer department that has a pumper with a two stage pump. I haven't used one of these since I was in the academy so I came up with a few questions.

First of all it is a 1000 GPM pump. If I remember correctly that is 1000 GPM @ 150 PSI with the transfer valve in the volume or parallel setting. When the transfer valve is in the pressure or series setting then you should get 500 GPM @ 300 PSI. Is this correct?

I was under the impression that when the transfer valve is in the volume setting then the pump works like a single stage pump and allows the pump to deliver its full rated capacity. The pressure setting is used to overcome friction losses in very long hose lays or high rise buildings. Is this correct?

A little background info. The department serves a residential/rural area with good hydrants in part of the district and no water in the rest. Most operations are done using the pumper drafting out of a portable tank, and tanker shuttles. Long hose lays are very rare, and when they do happen we use 5" hose.

They leave the transfer valve in the pressure setting, and they have since they got the truck 17 years ago. Everyone there learned with the transfer valve in pressure mode and were told never to touch it. I was taught that if you weren't going to use the two stage pump then to just leave the transfer valve in volume mode. Is this correct? The valve hasn't been moved in 17 years, so it probably won't move anymore. At least not without breaking!

When I questioned this practice and tried to dig to find out why they did this, no one knew. Anyone have any ideas why you might leave the transfer valve in pressure as opposed to volume setting all the time? The way I figure, the first due attack pumper now has the pump capacity of a brush truck.

Any input/suggestions would be greatly appreciated.

Thanks, 310

[Irish6019]

As per my proby manual you are correct. Volume mode as you say or gpm should be used most of the time. Except to overcome very long stretches or standpipes.

[ChiefKN]

Our policy is that it's left in Volume mode. That way, the worst case scenario happens and you need big volume, you'll always have that available.

Granted the truck's engine might have to work harder, but they are designed to run.

That doesn't mean that we won't use pressure mode, we will.

As for any advantage to leaving it in pressure? Don't have a good reason why for most departments. There may be some who do a lot of standpipe work, but even with the long lays, if you are using LDH, you probably should stay in Volume.

[txgp17]

What brand of pump is it?

We used to leave the pumps in Pressure Mode, but that's a personal decision. They were American LaFrance pumps, and those always started in volume regardless of the settings, and would only switched if you reached about 50 psi. 90% of the time you won't exceed half of the pump's rated capacity, so it benefits from being left in the pressure mode. Plus it creates less wear and tear on the engine.

If the truck has been service tested, it should have been switched at least once a year. Waterous recommends once a week. If it sticks, then dump a 1% concentration of mild dish washing soap into the booster tank. Circulate that thought the pump. Let it sit for a few days and retry. Also, try working all the bleeder and drain valves to make sure they work. I usually hook a garden hose into the pump to push out debris from the bleeders and drains.

[GTRider245]

We have one truck that has a transfer valve. Its a 2003 E-One with a Waterous 1250. It was speced that way. It stays in pressure mode unless volume is needed, which is almost never around here. You seem to have the basic concept down. In volume, you get less pressure but more GPM, and vice versa for pressure.

As far as the pressure setting overcomming FL in long layes, a relay pump should be somewhere on that line if it is that long. You mention that you use 5" hose. That almost completly takes away the issue of FL in supply line layes.

[rescue84]

My understanding is when left in pressure mode, that also works with the pressure governor. It builds the pressure by first impeller to second impeller then out pump discharge. The second impeller is building off of first impeller's pressure. GPM max is I think only 70-75% of pump max while in SINGLE stage, pressure/ series, have to switch to Volume to get the pump maximum.
The volume is for supply pumping to get the volume not so much the pressure. Inlet line splits to an open valve to divert intake to first impeller and around to second impeller then they flow separately to pump discharge manifold. The impellers work independently.
Pressure governor IS the OPERATOR in volume- pay attention.

don't mean to make it sound demeaning, just explaining it so if some one has no idea of the mechanics that may be reading later.

Please correct me if I messed up some where.

[MG3610]

I recently became involved with a volunteer department that has a pumper with a two stage pump. I haven't used one of these since I was in the academy so I came up with a few questions.

First of all it is a 1000 GPM pump. If I remember correctly that is 1000 GPM @ 150 PSI with the transfer valve in the volume or parallel setting. When the transfer valve is in the pressure or series setting then you should get 500 GPM @ 300 PSI. Is this correct?

I' think the answer here is relative to the actual pump itself and its efficiency. In pressure mode your output will be less and the pump pressure will be higher. Remember either way the numbers are relating to draft. From a sufficient pressurized source you will exceed the capacities on the rating plate no matter what mode you are in.

I was under the impression that when the transfer valve is in the volume setting then the pump works like a single stage pump and allows the pump to deliver its full rated capacity. The pressure setting is used to overcome friction losses in very long hose lays or high rise buildings. Is this correct?

Yes. You can also pump through 2 or 3 single stage pumpers in series to acheive the same principle as a single 2 stage pump if high pressures are needed from a single stage pump.

A little background info. The department serves a residential/rural area with good hydrants in part of the district and no water in the rest. Most operations are done using the pumper drafting out of a portable tank, and tanker shuttles. Long hose lays are very rare, and when they do happen we use 5" hose.

They leave the transfer valve in the pressure setting, and they have since they got the truck 17 years ago. Everyone there learned with the transfer valve in pressure mode and were told never to touch it. I was taught that if you weren't going to use the two stage pump then to just leave the transfer valve in volume mode. Is this correct? The valve hasn't been moved in 17 years, so it probably won't move anymore. At least not without breaking!

When I questioned this practice and tried to dig to find out why they did this, no one knew. Anyone have any ideas why you might leave the transfer valve in pressure as opposed to volume setting all the time? The way I figure, the first due attack pumper now has the pump capacity of a brush truck.

Any input/suggestions would be greatly appreciated.

Thanks, 310

..........

[MG3610]

My understanding is when left in pressure mode, that also works with the pressure governor. It builds the pressure by first impeller to second impeller then out pump discharge. The second impeller is building off of first impeller's pressure. GPM max is I think only 70-75% of pump max while in SINGLE stage, pressure/ series, have to switch to Volume to get the pump maximum.
The volume is for supply pumping to get the volume not so much the pressure. Inlet line splits to an open valve to divert intake to first impeller and around to second impeller then they flow separately to pump discharge manifold. The impellers work independently.
Pressure governor IS the OPERATOR in volume- pay attention.

Incorrect. A pressure governor senses the pressure in the discharge side of the pump and adjusts the engine speed to maintain that pressure. The governor has no idea what mode the pump is in.

don't mean to make it sound demeaning, just explaining it so if some one has no idea of the mechanics that may be reading later.

Please correct me if I messed up some where.

..........

[Rescue101]

A two stage,while it CAN do 300psi is not RATED at that pressure.In todays diesel world a two stage is basically unnecessary except for a few special circumstances.They were more widely used in the Gas engine era when proper use could save a bunch of fuel and engine wear.We've used them for over a half century but our next one WON'T be two stage.No real tricks to use,if you can't get the flows you need in pressure setting,throttle down and switch to volume(oversimplified). T.C.

[CMM310]

Thanks to everyone for their replies.

I appreciate the information.

I spoke with a member that has been here since the very first fire truck was delivered in the town. He told me that they got the two stage pump since they had always had them on the older gasoline powered engines.

The idea behind leaving the pump in pressure mode is because the pumper almost never pumps close to half of its capacity.

Last night we grabbed a state fire instructor who is familiar with two stage pumps, got the transfer valve working and went out and played with flowing different amounts of water in both pressure and volume modes and began to see when we would need to switch from pressure to volume.

More training is scheduled for all pump operators in the near future.

Thanks for your help, 310

[LeatherHed4Life]

we had a 2 stage for a while, and we kept it in pressure until we flowed more than 700 gpm, then we would switch the second stage on. for similiar reasons the truck rarely would be pumping half its capacity. It was good to practice either or.

[chrissoda7800]

Volume should be used anytime that your pumping more then half the pumps rated capacity. Example 1200 GPM pump, when your flowing more then 600 gpm you should be in volume.
Pressure setting should be used anytime that your pumping over 200 psi.
As far as the pressure governor goes, I'm assuming that there are two settings, RPM and Pressure. When in the RPM mode, you're not using the pressure relief valve. When you have it in the Pressure setting you are using the pressure relief valve. I'm assuming you don't have a manual pressure relief valve.

[MG3610]

The electronic governors that utilize a PSI/RPM mode do not provide any sort of relief valve type function. They simply regulate the engine speed. In PSI mode they regulate the speed of the engine based on maintaining the pump pressure to whatever you have it set to and in RPM mode you are only setting the engine to maintain a specific RPM.

Some companies are still specing discharge relief valves, and apparently its becoming common with CAF rigs too, because the governors are being kept in RPM mode to operate the compressor effectively from what I understand.

[Ha11igan]

Volume should be used anytime that your pumping more then half the pumps rated capacity. Example 1200 GPM pump, when your flowing more then 600 gpm you should be in volume.
Pressure setting should be used anytime that your pumping over 200 psi.
As far as the pressure governor goes, I'm assuming that there are two settings, RPM and Pressure. When in the RPM mode, you're not using the pressure relief valve. When you have it in the Pressure setting you are using the pressure relief valve. I'm assuming you don't have a manual pressure relief valve.

Wrongo. When DRAFTING more than 600 gpm, not flowing. I've seen much more than the rated capacity being flowed while in pressure/series mode.

[kuh shise]

When operating one or two preconnected lines with flow totals under 400 gpm, the engine will run slower in the pressure mode. You can try this yourself by starting out with a single PC and record the engine RPM. Then switch to the volume position and again develop the desired discharge pressure and note the required RPM to reach the proper discharge pressure. Continue to add discharges in 100 to 150 GPM increments and perform the same comparison. Depending upon the pump casting, somewhere around 50% of the rated capacity of the pump, you should begin to notice that the pressure position requires higher RPM to deliver the desired flow at the correct discharge pressure. Working from the apparatus tank usually results in better motor speed if you are in series (Pressure) mode.
When being fed from a good hydrant, sometimes the discharge pressure on a single PC line will exceed the desired discharge pressure, even at idle. Then it could be better if you were in volume, as this will allow you to raise the RPM above the idle speed and improve operating conditions for the motor. The other method that will work on an engine equipped with a relief valve is to waste the motor horse power by setting the relief and over pumping the system. This is hard on the relief to be constantly in the open mode, but we have used this method with CF Macks for years. Mack did something interesting with the Watrous two stage. They tapped the volute on the first stage and used it to feed the tank fill. This works great when filling direct from a hydrant W/O running the pump, but is a disaster if you are depending upon the tank fill to cool the pump. This arrangement blocks any flow through the second stage of the pump unless the nozzle is flowing water. We run all our engines in the pressure mode until we get at least 3 lines operating. I agree with several comments on this forum concerning the need or lack of need for a two stage pump with a good diesel motor. The original idea behind the 2 stage pump was to allow gasoline engines to operate in a much narrower and higher RPM range. Because we now have low speed high torque diesel engines with fairly flat operating curves, it is no longer necessary to specify 2 stage pumps unless very high discharge pressures will be the normal operating requirement. LDH and preconnected hose lines seldom require discharge pressures over 200 PSI, except for certain high rise stand pipe feeds.

[bobsnyder]

I've seen much more than the rated capacity being flowed while in pressure/series mode.

This is really one of those things where "individual results may vary" applies because there are so many variables that go into actual pump performance. I think it is fair to say that a very good rule of thumb is that your 2-stage pump will flow rated capacity in volume and half of rated capacity in pressure. That said, I know our 2000 gpm 2-stage engine will move 2250+ gpm in volume and max out a 1250 gpm supply pumper while still in pressure. Our engine is set up in pressure mode by default, which is fine because we could run all four crosslays at 200 gpm and still not exceed the rated capacity in pressure mode. Volume is something we generally don't even think about using unless we're looking at master stream operations, tanker filling, or something of that sort. Again, that's with a 2000 gpm rated pump that we know will do 1200+ gpm from a non-static supply in pressure mode.

I agree with several comments on this forum concerning the need or lack of need for a two stage pump with a good diesel motor...Because we now have low speed high torque diesel engines with fairly flat operating curves, it is no longer necessary to specify 2 stage pumps unless very high discharge pressures will be the normal operating requirement. LDH and preconnected hose lines seldom require discharge pressures over 200 PSI, except for certain high rise stand pipe feeds.

That pretty much sums it up.

Some companies are still specing discharge relief valves, and apparently its becoming common with CAF rigs too, because the governors are being kept in RPM mode to operate the compressor effectively from what I understand.

I never even thought about that...Hmmmm...