Drafting in RPM mode only

[shaines]

i have been told that with a Class 1 electronic control to draft only the RPM mode and not the Pressure mode. i have read many things that indicate that it would be eaier to lose a draft or fill in pressure mode (because any amount of air would cause the electronics to believe that the water supply has been lost and go to idle to protect the pump). i think I understand this.

i have been told that there is potential for tank damage if doing this in pressure mode. I just can't figure out how this is possible.


Steve

[nmfire]

Tank damage?? Geez, I guess we better take every engine and tanker made in the last 30 years with a mechanical vernier throttle out of service. Sounds like BS to me.

You will NEED to establish and get going in RPM mode. PSI mode by its very nature will not work during this phase. I set no less than 1,000rpm while establishing a draft and maintain that until I have it sucked up and flowing. Once you have a good solid draft, you can use PSI mode without a problem. Its like with ANY water source including tank water and hydrants when using PSI mode. If that water supply starts getting funky on you, you better be ready to take over.

[MG3610]

It is a fact that using RPM mode is either a good idea in principle, or in some cases recommended by manufacturers.

The Pressure sensor is sensitive to air. Several different responses are possible by the electronic system upon loss of prime or air entering the system. They include but are not limited to...

Air in pump: pump Fluctuates RPM (and also PSI). Pump drops to idle if it doesnt sense increase of discharge pressure. Pump reduces to a set RPM or Pressure and will not increase until operator intervention

Momentary Loss of prime-complete-followed by return of water flow: Attempt by system to raise RPM until lack of increase in pressure is noted by the electronics. Remember, the governor will raise RPM in PSI mode until it realizes there is no corresponding pressure increase then will respond to the condition.

When a brief water interruption occurs in PSI mode, the engine RPM will begin to increase, if the water supply is reestablished prior to the RPM returning to idle (as it should after a certain time period without water or with entrained air) the water coming into the pump can be sent back out in a pressure spike because the electronics cannot respond fast enough.

Stick to RPM for drafting, otherwise you could have alot of crazy dancing gauges and a cool fire hose rodeo.

http://www.class1.com/_Downloads/cla...rs,%20FAQs.pdf

[txgp17]

You only have to be in RPM mode if you intend to idle up before getting a prime.

Once the pump is primed and flowing, doesn't matter what mode it's in. If you have a small air leak, it's no big deal as long as you continue to flow water.

A centrifugal pump won't pump/move air, but it will pump air AND water together.

[farmerfire1156]

I have a question in line with this. We have one Darley with electric primer, the manual states to not engage the pump till post prime??? Why exactly is that??

[chiefengineer11]

I have a question in line with this. We have one Darley with electric primer, the manual states to not engage the pump till post prime??? Why exactly is that??

Wow, how old is that pump. In the days of pumps and transfer cases where you had prime gear and pump gear, the prime (vacuum) line entered the pump at the top of the pump case so that you filled the entire pump case with water. The impellers were stationary during priming. You put the pump in "Prime" gear, got your prime before shifting to "Pump" to start the impellers turning to begin flowing water.

In today's pumps, wher the impeller(s) is (are) already turning, the prime line enters the case near the eye of the impeller. Many years ago David Sargeant of Waterous Co. (I think) wrote a paper on the difference and the physics of why it is done that way.

So the only reason I can think of is that the prime line enters the pump case at the top.

On having to be in RPM mode, I agree with txgp17. The electric motor driven and air primers are not dependent on engine RPM to pull a prime. You can prime at idle or theoretically, even with the engine shut off completely. But if you want to bring the pump speed up above engine idle, then RPM mode is in order.

[farmerfire1156]

Chiefengineer, can you pm me at bugfarmer1156@yahoo.com?

[MColley]

This is how it was explained to me and what I understand from the manual.

In PSI mode the govenor responds to increases and decreasses in PSI when the pressure is above 70 PSI.If there is a fluctuation and the govenor cannot regain PSI within 4 seconds it will flash INTAKE and then reduce PSI to the last point the pressure was achived. (In a drafting operaton this probably won't happen because the pressure would be in the negitive to start with)

Second And this is the big reason.

If pump discharge pressure drops below 30PSI for more than 5 seconds, the govenor will return the engine to idle and LOSUPPLY will be displayed. The govenor then enters it's initial power up state and you need to start over.

That being said this all happens when the govenor control is set in PSI mode. So basicly unless you can get a draft in about 4 to 5 seconds the pump is not going to sense any pressure and return to idle. When you place the govenor control in RPM mode it over rides the low pressure sensor and allows you to maintain a steady RPM and create a draft without the risk of the control shutting the govenor down.

As for pumping in PSI mode while drafting. I would recomend against it as your pump will get fluctuations in PSI and it will try to correct them and probably be idleing up and down constently trying to maintain a working pressure. Our SOG is to run the pump in RPM when drafting or working a relay and maintain pressure manualy.

[chiefengineer11]

Chiefengineer, can you pm me at bugfarmer1156@yahoo.com?

I did, yesterday. Did you get it?

[FyredUp]

I just ran a pump operator class the other night where we did drafting ops, pumping multiple lines, deck guns, and relay ops.

I totally agree with beginning the drafting op while in RPM mode. But once you have established draft and set your discharge pressure and set the individual flows there is no reason not to switch to psi mode.

We successfully ran multiple lines, deck gun, and a short relay from draft. We did start out in rpm mode to get the draft started, then set our highest discharge pressure and the individual discharge pressures and once things were set and stabilized we switched to psi mode. There were no issues what so ever.

Frankly, if running out of water is an issue it won't matter what mode you are in because you are still out of water.

[chiefengineer11]

This is how it was explained to me and what I understand from the manual.

As for pumping in PSI mode while drafting. I would recomend against it as your pump will get fluctuations in PSI and it will try to correct them and probably be idleing up and down constently trying to maintain a working pressure. Our SOG is to run the pump in RPM when drafting or working a relay and maintain pressure manualy.

I'm not following your logic on this. When you are in PSI mode and set your discharge pressure (as FyredUp points out, set for the highest line pressure and gate down for other lines needing lower pressures), the system will do what it has to to maintain that set pressure. Assuming you have an adequate water supply, as lines are opened and closed, more or less engine RPM is needed to maintain the set pressure. The system will read in and tell the engine what to do to maintain that pressure. The change in engine speed is the pressure governor doing its job. If the system is functioning correctly, any variation in pressure will be minimal and very brief. It reacts the instant a change takes place. People manning hand lines should not notice any change.

Compare that with trying to keep up manually. You, the pump operator have to see or hear a change in what is happening and react to that change. You have to manually move the throttle control up or down as indicated, and guess at how much to move it.

In a true manual throttle system that so many people would like to go back to, any change in water flow will cause the engine RPM to increase or decrease, so the change to the remaining lines can be pretty radical. In an electronic system in RPM mode, the engine RPM won't change, so the change at the nozzles won't be as radical as with a true manual system. But there will be some change to nozzle pressure.

We first got into pressure governors with our '89 Quality/Duplex. It has a mechanically operated 6V92TA Detroit, and a Barber-Colman governor system. We have one operator who just could not accept that this thing would do its job. Every time somebody went to open or close a line, he was reaching for the throttle control. I almost had to stand there with a baseball bat to make him keep his hands off of it. He's a chief now, so most of the time I can keep him away from the pump panel altogether.

[kuh shise]

When supplying attack lines while drafting from a port-a-tank, it is proper to set the governor in the PSI mode to control the line pressure. Not any different than operating off tank water.
When supplying a relay operation, the supply and any relay engines should be set to RPM mode. I will attempt to describe what happens if both the supply and attack engines are set to “Pressure” mode.

First assume that you have been able to establish a non-fluctuating flow. That is one where all attack nozzles are operating and both engines are throttled up providing a consistent flow. Now lets shut down one of the attack lines. We get an increase in discharge pressure that is countered by the governor throttling back on the attack engine RPM to reach the set pressure. This takes several seconds and results in the discharge coming back to the set pressure, but the intake pressure has risen due to a decrease in friction loss in the supply line caused by the lowered flow volume. This pressure increase is transmitted back through the hose to the supply engine, but at a delayed time due to expansion of the hose. The supply engine’s governor now decreases the discharge pressure bringing the discharge back to the set pressure. This action lowers the intake pressure on the attack engine (after a little delay due to hose contraction) causing the attack engine to again increase rpm to compensate for the lowered intake pressure. This drops the intake pressure sending a lower pressure back to the supply engine. Now we have set up a war between the two governors. The longer the lay and the larger the diameter of the supply line, the larger the surge pressure that is developed, and the longer the time period between surges. It is best to control the supply engine and any relay engines in the RPM mode. Even better would be to drop a Port-a-pond at the attack engine, connect a hard sleeve to one side of the engine, and bring the relay water into the opposite side of the engine then allow the pump operator to control the flow from the relay through the intake valve.
When connecting multiple engines in a relay situation, think like every engine throttle must be slaved together. Every throttle move that one operator makes must be followed by similar actions by all the other operators. A three or 4 engine relay might have several thousand horsepower tied into the system.

[MColley]

I understand the points made.....Mayeb I'm just still a little old fashon and don't trust the control as much as I should....However to go with my statemend about being in PSI mode while drafting. A good stable water source yes you could be in PSI drafting from a port-a-tank. I wouldn't simply becuase if you jet syphone you will get air pockets in the draft line and even worse if you have to dump directly into the port-a-tank you are drafting out of. I know it doens't seem like there would be enough air mixed in to make a differnce but I notice huge differnces and I have had the pump shut down in PSI mode because of this.

[chiefengineer11]

When supplying attack lines while drafting from a port-a-tank, it is proper to set the governor in the PSI mode to control the line pressure. Not any different than operating off tank water.
When supplying a relay operation, the supply and any relay engines should be set to RPM mode. I will attempt to describe what happens if both the supply and attack engines are set to “Pressure” mode.

First assume that you have been able to establish a non-fluctuating flow. That is one where all attack nozzles are operating and both engines are throttled up providing a consistent flow. Now lets shut down one of the attack lines. We get an increase in discharge pressure that is countered by the governor throttling back on the attack engine RPM to reach the set pressure. This takes several seconds and results in the discharge coming back to the set pressure, but the intake pressure has risen due to a decrease in friction loss in the supply line caused by the lowered flow volume. This pressure increase is transmitted back through the hose to the supply engine, but at a delayed time due to expansion of the hose. The supply engine’s governor now decreases the discharge pressure bringing the discharge back to the set pressure. This action lowers the intake pressure on the attack engine (after a little delay due to hose contraction) causing the attack engine to again increase rpm to compensate for the lowered intake pressure. This drops the intake pressure sending a lower pressure back to the supply engine. Now we have set up a war between the two governors. The longer the lay and the larger the diameter of the supply line, the larger the surge pressure that is developed, and the longer the time period between surges. It is best to control the supply engine and any relay engines in the RPM mode. Even better would be to drop a Port-a-pond at the attack engine, connect a hard sleeve to one side of the engine, and bring the relay water into the opposite side of the engine then allow the pump operator to control the flow from the relay through the intake valve.
When connecting multiple engines in a relay situation, think like every engine throttle must be slaved together. Every throttle move that one operator makes must be followed by similar actions by all the other operators. A three or 4 engine relay might have several thousand horsepower tied into the system.

When we got our first engine with a pressure governor, surges and resultant "hunting" or wars between governors in relay operations was one of my concerns. Now I will certainly admit that due to the way our local and mutual aid areas are situated and with the water supplies in them, long relay operations are rare. But with the limited opportunities we've had, that has not been our experience. In the very few that I've done with each of our two very different governors (Barber-Colman and FRC Pump Boss), both as an attack engine at the end of a relay, and as a relay engine, both governors have performed flawlessly.

[rfdffemtmpo]

I have a question in line with this. We have one Darley with electric primer, the manual states to not engage the pump till post prime??? Why exactly is that??

We have multiple Darley engines. I think what they are trying to say, is to connect your suction hose to your dry hydrant or whatever you're using, and pull the primer without the pump in gear to get water up to the pump. Once you have water to the pump, you would then put it in gear and run it.
That method described would work great for a fill site, but not a fire attack pumper. When responding on fires, we always start on the tank, and switch to a drop tank.
If your Darley has their electronic pressure governor, this thread has great info. Make sure to start drafting on RPM mode. The control (in psi mode) will look for 45 psi or greater once the pump is in gear. If this is not achieved, the control will enter a no water mode. If you are pumping and the discharge drops below 45, it will enter a low water mode which results in it going to 1100 rpm for 7? seconds. If no increase in discharge, it will go to no water mode and go to idle.
I am attending Darley's CAFS academy in a few weeks. I will ask them their opinion on this subject.

[farmerfire1156]

We have multiple Darley engines. I think what they are trying to say, is to connect your suction hose to your dry hydrant or whatever you're using, and pull the primer without the pump in gear to get water up to the pump. Once you have water to the pump, you would then put it in gear and run it.
That method described would work great for a fill site, but not a fire attack pumper. When responding on fires, we always start on the tank, and switch to a drop tank.
If your Darley has their electronic pressure governor, this thread has great info. Make sure to start drafting on RPM mode. The control (in psi mode) will look for 45 psi or greater once the pump is in gear. If this is not achieved, the control will enter a no water mode. If you are pumping and the discharge drops below 45, it will enter a low water mode which results in it going to 1100 rpm for 7? seconds. If no increase in discharge, it will go to no water mode and go to idle.
I am attending Darley's CAFS academy in a few weeks. I will ask them their opinion on this subject.

Yeah, That is what we have been reading as well. Let us know what they say.

[farmerfire1156]

I did, yesterday. Did you get it?

negative, bugfarmer1156@yahoo.com

[shaines]

I understand the whys of achieving a draft in RPM mode (air, idle etc...) The part I am missing is why I am told that there is potential for tank damage if doing this in pressure mode. I just can't figure out how this is possible.

Any thoughts on the tank damage part of this?

[kuh shise]

A tank with inadequate vent size can cause excessive internal tank pressure if filling the tank at high rates. It would not be any more likely at draft than when being supplied by a hydrant. Suppose we had a 2 inch pump to tank line that was relatively short. ( 3' or less) Hazen-Williams or even calculations of friction loss for 2" hose will show that it is possible to reach 1,000 gpm fill rate at reasonable pump pressures. Using our 1,000 gpm fill rate the air will easily escape, but the vent size (diameter) will act like a nozzle. The formula for nozzle flow is 30 x D x D x Sq. Rt. of Nozzle pressure. Working backwards using 1,000 gpm flow and a 4" vent you will find a nozzle pressure of 4.34 psi. This might seem like a small pressure, but the tank top can easily be 5 ft wide and 10 ft. long, or 50 sq ft of lid surface area. Since our pressure is in PSI, we need to convert this 50 sq ft to sq inches. (multiply by 144 sq in / sq ft) Area will be 7200 sq in and the pressure on the lid will be 31,250 lbs. For similar reasons it is necessary to have large vents on tanker (tender) apparatus to prevent damage to the tank or injury to personnel.

[rfdffemtmpo]

I have a question in line with this. We have one Darley with electric primer, the manual states to not engage the pump till post prime??? Why exactly is that??

I went to the CAFS class and asked them about this. The answer they gave me was it is more of a safeguard so that the pump doesn't run without water for more than 20 seconds. The example they used was that if you were to put the pump in gear, try to hook up the suctions, and have a problem drafting from air leaks or drains open, the pump would run too long without enough water. They said that this is a recommendation, not a rule written in stone, they just want the pump to have prime or a good water source within 20-30 seconds.