RPM Mode Vs. Pressure Mode on a Tanker

[txgp17]

As well as if you are any truck in a relay other than the attack engine.

I disagree, there is no pressure protection for the other engines, aside from their own intake relief valve, unless you have a governor and a discharge relief valve, which is extremely rare.

If all the pumps in a series are cranked up to 3,500 RPM (that's pump speed, not engine speed), and the attack engine suddenly reduces his flow, then the friction loss instantly disappears. But the governor keeps the pumps cranked up at a high speed. You go from having a relay to giant 3 or 4 stage pump. That is dangerous.

Centrifugal pumps are known for their ability to take advantage of intake pressure, and their ability to add net pressure to the water. When the friction loss is removed, this pressure compounds with each impeller in the system. Something has to give, and it might be something you were counting on.

When you're in a relay, your governor should be in the PRESSURE mode.

[MColley]

I have heard from a few people say with the class 1 governor's that if you are drafting water you should use the RPM mode, is this true? or has anyone else heard this?

Yes that is true. We run 2 apparatus out of our station with class 1 governor controls. And you should be in rpm mode to draft. As well as if you are any truck in a relay other than the attack engine.

[16Scott]

Tankers and Governors

. . ."Pump in "pressure" mode. That is the main point. With most set-ups, is the only way that your pump governor is going to work properly."

I disagree but let me explain. If your tanker is supplying an engine also equipped with a governor, the engine should definatelt be pumping in "pressure." However, the tanker (or any other apparatus that is supplying an engine) should pump in "RPM" mode. The tanker has no need to regulate pressure - that is the job of the attack engine. With both governors trying to regulate pressure you may experience constant pressure oscillations as the two pumps try to "battle it out" in an effort to maintain pressure.

. . ."I have heard from a few people say with the class 1 governor's that if you are drafting water you should use the RPM mode, is this true? or has anyone else heard this?"

It is theoretically impossible to draft in PSI mode because the pump is dry. The PSI mode utilizes a pressure sensor (transducer) inside the discharge manifold. When the pump is dry the transducer reads ZERO pressure which will not permit an increase in RPM. Drafting in RPM mode turns off the transducer. Following a successful draft and charging lines, change to PSI.

[16Scott]

Clarifying pressure vs. RPM for Tankers

. . ."Pump in "pressure" mode. That is the main point. With most set-ups, is the only way that your pump governor is going to work properly."

I disagree but let me explain. If your tanker is supplying an engine also equipped with a governor, the engine should definatelt be pumping in "pressure." However, the tanker (or any other apparatus that is supplying an engine) should pump in "RPM" mode. The tanker has no need to regulate pressure - that is the job of the attack engine. With both governors trying to regulate pressure you may experience constant pressure oscillations as the two pumps try to "battle it out" in an effort to maintain pressure.

. . ."I have heard from a few people say with the class 1 governor's that if you are drafting water you should use the RPM mode, is this true? or has anyone else heard this?"

It is theoretically impossible to draft in PSI mode because the pump is dry. The PSI mode utilizes a pressure sensor (transducer) inside the discharge manifold. When the pump is dry the transducer reads ZERO pressure which will not permit an increase in RPM. Drafting in RPM mode turns off the transducer. Following a successful draft and charging lines, change to PSI.

[ccfdblehman]

I thought priming pumps were rotary vane pumps not piston pumps...

Or are there some of both?

[KuhShise]

Pressure relief and pressure governor - Pa. Fire Academy

Back when "Mac" first got the KME for the academy at Lewistown, he encountered this same problem, so both systems were installed to prevent the spike at change-over.

[bobsnyder]

I have heard from a few people say with the class 1 governor's that if you are drafting water you should use the RPM mode, is this true? or has anyone else heard this?

I prefer it. If you're working in pressure mode and you have a problem pulling a draft for some reason (or a problem develops after you do), the pump can momentarily "run away" on you (until it hits the engine governor and the system shuts itself down). In RPM mode, this won't be an issue.

I've never seen a governor system with a pressure relief valve, let alone an automatic one. What's the point of having both?

I actually know exactly where to find a few. These companies put the pressure relief on the pump to serve as a safety against surges when using handlines. Don't forget...a pressure governor maintains pressure by adjusting engine RPMs to match its pressure setting. If a hydrant or a supply pump operator hit it with enough pressure on the incoming side, the pressure governor can do only so much, so fast to stop it. Once the incoming pressure overcomes the pressure goveror, it's all over and you need a direct mechanical means (gating back on valves, etc.) to control the pressure. An intake relief valve wil do almost the same job by defending against incoming surges or overpressurized lines, but won't help you with runaways during drafting, or similar malfunctions.

[nuthead]

Dacron hose, not leather? What is next, getting rid of rotary and piston pumps?

Piston pumps still have their place....for priming the pump.

[KuhShise]

Change-over Pressure spike

jercvfd:

The original pressure governor designed by hale in the 1950's were all installed on gasoline engines. When the throttle was decreased by the spike in pressure as you changed over from tank water to hydrant water, the throttle plate closing caused a vacuum increase in the intake manifold. This vacuum is applied to the pistons during the intake stroke, while the crank case breather allows atmospheric pressure to be applied to the bottom of the piston. The differential pressure immediately slows a gasoline engine. Since pump discharge pressure is proportional to rpm, you get an almost immediate reduction in pump discharge back to the set point.

A modern diesel engine has a turbo that is stuffing fresh air into the "inter-cooler" and then into the intake of the engine. You might think of the intercooler as an air tank that will continue to push the engine around until the rpm's coast down to the set point. Something like not using an engine brake on a down hill. The diesel will continue to roll, but a gasoline engine will slow down.

The installation of a pressure relief valve would solve your problem if the pump operator had set the relief valve just above the desired set point for the preconnect lines. We have modified several of our engines by adding relief valves in our own shop. Your pump operators need to be instructed how to use the relief along with the Class I pressure governor, because it is very easy to set-up a war between the two different controllers. If your engineers decide to install a relief valve system, I would suggest using a Hale relief, since the Watrous works in a way that could make it fail in the open position thus preventing the engine from building pressure.

Kuh Shise

[edge1317]

No what haweater was saying when your hydrant man connects you to the hydrant and opens the hydrant ITSELF. That if he opens it very slowly that the pump won't have such a surge and will have less pressure to readjust itself over time.

Also, did you try the relief valve?

[jercvfd]

We have tried reducing pressure beforing taking hydrant water but no considerable difference. The only way we have been able to switch from the tank to a hydrant without getting the spike is to idle the truck and then switch over. Problem is u can not do that with guys in a structure. I think maybe part of the problem is the intake and the tank to pump are electric, there is no opening them slow , but thanks for the advice

[Haweater]

Last year our dept. took delivery of a new pumper that has an rpm/pressure governor. Our problem is when we are in pressure mode and running off of the tank of the engine, when we open the hydrant and switch from tank to hydrant we get a spike in pressure of about 230lbs for about 3 or 4 seconds with the governor set at approx. 130 lbs. The pump and the governor manufacture say that there is nothing we can do about it. They tell us that the governor can not compensate for the momentary pressure increase when we open the hydrant.It is a waterous pump and i think it is a class III governor? Wondering if anyone else has had that problem.

Try opening the valve for hydrant water in sloooooooowly

[edge1317]

You could switch to RPM mode when you open the hydrant and bring the RPMs down coordinated with the opening of the hydrant, but you'll still get either a pressure loss or increase, depending or fast/slow you are.

Edit-Just thought of another way, you could set your relief valve at your current pressure and you'll just dump out the pressure during the switch.

[jercvfd]

Last year our dept. took delivery of a new pumper that has an rpm/pressure governor. Our problem is when we are in pressure mode and running off of the tank of the engine, when we open the hydrant and switch from tank to hydrant we get a spike in pressure of about 230lbs for about 3 or 4 seconds with the governor set at approx. 130 lbs. The pump and the governor manufacture say that there is nothing we can do about it. They tell us that the governor can not compensate for the momentary pressure increase when we open the hydrant.It is a waterous pump and i think it is a class III governor? Wondering if anyone else has had that problem.

[FFmedicGUMP]

easy way is this:
thinking of it like banging some chic (fat chic in my case)
rpm or revolutions per minute is how many times you hump her in one minute
psi is the pressure, or force, you use.
so do you want to hump her 40 times, aka 40 rpm, or try and break her pelvis, aka lots of pressure