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    Default newbie question re pumping in volume

    I'm a newbie to pumping and i had a question that i couldnt find an answer to online so far. I understand the idea behind pumping in volume (the impellers running in parallel etc) but I was wondering if the gauges (intake and discharge) show a different reading when pumping in volume compared to pumping in pressure. Also can you switch between the two while in operating lines or do you have to shut down your discharges before switching over. Sorry for the newbie question. thanks.

    also one last question. Do you have to set the pressure relief valve if you are using 2 or more lines operating at the same pressure?
    Last edited by barnyard2; 11-03-2009 at 01:02 AM.

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    I don't use 2 stage pumps so I'll let someone else answer that.


    You should always set the pressure relief valve. Having multiple lines off makes it especially important, if both lines are operating and 1 shuts down abruptly it can spike the pressure in the other line.

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    Quote Originally Posted by barnyard2 View Post
    I was wondering if the gauges (intake and discharge) show a different reading when pumping in volume compared to pumping in pressure. Also can you switch between the two while in operating lines or do you have to shut down your discharges before switching over.
    Pressure is pressure, no matter what mode you are pumping in. Gauges will read whatever you are discharging- Remember when you are in volume, your discharge pressure will drop.

    Modes can be changed with water flowing, although I would be hesitant to go from a higher pressure back to volume without throttling down. Making the changeover at a high pressure could be exciting!
    "Loyalty Above all Else. Except Honor."

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    There is huge difference when pumping in pressure or volume mode. In pressure mode, lets say your pumping out 150psi at the discharge gauge. As soon as you flip the transfer valve over to volume, it will go down to roughly half that, to about 75-80 psi. As for the PRV, this isn't a big deal, at the end of the hose, it is.

    Now making the transition from volume to pressure, there alot of bad things that can happen to the guys on the other end, that are not expecting it. Try it once training, and you'll find out. As well, you will find that having the PRV set to where you want it, will keep the hose from flying out of your guys hands. This is in reverse of the above.

    So if your pushing 100 psi in volume mode, and have your PRV set at 150, when you change your transfer valve to pressure, it will want to go up to aprx 200psi at the gauge. But with the PRV set at 150, it will spike to about 160-170 psi, and then drop to your setting. This happens to keep the guys safe and still able to hold the lines.

    What ever you do, ALWAYS make sure your hose guys know what your doing. If not, bad things can happen.

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    "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

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    As with many of us, I go back to the days when relief valves and hand throttles were the norm. And as both Buff and FireMech have said, things could get pretty exciting if you didn't get it right.

    With today's electronic throttle controls (assuming they're working correctly) the changeover is pretty seamless. We have a Barber-Colman unit on a 6V92 Detroit mechancal engine and a FireResearch Pump Boss on an electronic C13 Caterpillar. With either one, as you make the switch from Volume to Pressure or vice-versa, the control makes the compensating engine RPM change.

    One other corollary point - when to change. Many people will tell you that it's right at that 50% point. That is, when you are flowing 50% of the rated capacity of the pump, change over. That's a good time to start thinking about it, but experience shows that it's not an exact figure. Depending on your source of water (drafting or being supplied and at what pressure) it can be anywhere between 50 and 70%. The rule I use is, if you think it's time to change, do it, watching your engine RPM and discharge gauge. Whichever mode gives the same pressure at lower engine RPM is the mode you want to be in.

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    Quote Originally Posted by FIREMECH1 View Post
    There is huge difference when pumping in pressure or volume mode. In pressure mode, lets say your pumping out 150psi at the discharge gauge. As soon as you flip the transfer valve over to volume, it will go down to roughly half that, to about 75-80 psi.
    FM1
    So would i have to throttle up to get back to 150 or is the line that was being pumped at 150 in pressure mode now SHOULD be pumped at 75-80 PSI in Volume mode

    btw...just for your info i am using an older engine where its a manual throttle control

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    Quote Originally Posted by barnyard2
    So would i have to throttle up to get back to 150 or is the line that was being pumped at 150 in pressure mode now SHOULD be pumped at 75-80 PSI in Volume mode.
    If your in pressure mode and change over to volume mode your going to lose pressure, both at the pump, and on the hoses. If you need to maintain 150psi, you will need to throttle up.

    FM1
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    Quote Originally Posted by EastKyFF
    "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

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    Going from series (pressure) to parallel (volume), as FIREMECH states, will lower the discharge pressure (by about 1/2) and might place the attack line in danger if they are using automatic nozzles since it is possible to drop below the 100 psi minimum on the line. After the change you will need to throttle up to reach the desired setting. Going from volume to pressure without reducing the rpms can cause some undesireable effects, particularly with pressure governors. The larger motors with large inter coolers between the turbo and intake can cause some pretty significant pressure spikes on the attack lines. It also causes the clapper valves in the pump to be violently slammed shut. These are usually cast iron and do not react well to this sort of treatment. It is better to throttle down before making a change over to avoid spikes and water hammer in the system.
    The gauges (master intake and discharge) are plumbed into the intake manifold at the firststage and the discharge master gauge is plumbed into the main discharge manifold thus the pressures are taken at the same point no matter what the pressure / volume setting is on the engine. You should not shut down any line that is attacking the fire unless specifically ordered to do so by the attack crew or an officer. (exceptions might be a wild line or blown hose that is endangering personnel) There are cases where the volume mode is preferable to the pressure mode at low application rates. Take the case of an engine that develops 80 psi at idle in the pressure mode. Supplying a 150 psi preconnect will be impossible if the incoming supply pressure is 70 psi or greater. Let's say that the hydrant is giving an incoming pressure of 110 psi. Then the 80 psi developed at idle will yield a discharge pressure of 190 psi on the line. This might be a little too much for the crew to handle especially if trying to climb a stair and flow water at the same time. We could gate the discharge back thus reducing the line to the desired 150 psi. However, at idle we might not have enough rpm to keep the alternator aor a pto generator operating properly. Switching to volume at about 1/2 the original 80 psi idle pressure (now 40 psi in volume) will bring the discharge back to 150 psi and allow the throttle to be raised up without over pressurizing the attack line.

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    Default Check with the Manufacturer

    I think everything has pretty much been hit on. My only suggestion about switching over would be check out what the manufacturer has to sa about it. When to do it,what pressures to do it at that kinda thing.

    The two stage I have here is supossed to be throtled way down before you switch it either way. It's like this becuase it is a air driven switch that is fairly quick and it helps to prevent damage to the pump.

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    Quote Originally Posted by MColley View Post
    I think everything has pretty much been hit on. My only suggestion about switching over would be check out what the manufacturer has to sa about it. When to do it,what pressures to do it at that kinda thing.

    The two stage I have here is supossed to be throtled way down before you switch it either way. It's like this becuase it is a air driven switch that is fairly quick and it helps to prevent damage to the pump.
    I'd be interested to learn what pump that's on, and how well it works. We had a 1978 Hahn with a Hale QLD pump. The transfer valve was operated by discharge pressure against a piston. It worked well as long as you had 50+ psi greater pressure on the discharge side of the pump than on the intake side. Trouble is, with our monstrous hydrant pressures (185+ on large mains), we rarely had the differntial, so the transfer valve wouldn't operate.

    After fighting with it for years, I finally replumbed it to operate with air rather than water. As an air source I teed into the road to pump shifter, which was air operated. As you mention, it transferred instantly. There was no slow motion involved. I tried putting different orifices in the air supply line to slow it down, but to no avail. It still transferred immediately, or not at all. So I left it alone, and it worked for as long as we had the truck.

    The only thing with it that I never was able to do anything about was that the air had to vent somewhere. Using the Hale valve, there was always a small flow of air from the tank to atmosphere when the pump was engaged. But since the system worked reliably and the air loss was tolerably small, I left it go.

    I wonder how yours is done.

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    We don't have any two stage pumps anymore, but our old two stage 750GPM required that you throttle nearly all the way down before making the swith...the transfer valvle wouldn't move if there was much pressure on it.

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    I can only speak for Waterous pumps, but ours can be changed at pressures of up to 250 psi without damaging the equipment. Today's new electric actuators can handle an awful lot.

    That said, when I'm training operators I generally tell them that throttling down to 75psi before changing either direction is a good idea. It is always best to assume that the relief valve may not be set properly when making these kind of changes to an operating pump, and therefore for the safety of any firefighters on handlines it is a good practice to throttle down before making the switch.

    My opinion has always been that it's better to loose some pressure on the line for a few seconds than it is to potentially have a dangerous pressure surge that could cause the loss of control of a handline.

    All that set aside, here is what is in our operating instructions:

    Switch transfer valve to desired position.
    NOTE: As a general rule, keep the transfer valve in
    PRESSURE (series) position when pumping up to
    2/3 of the rated capacity of the pump and in VOLUME
    (parallel) when pumping more than 2/3 of the
    rated capacity. If the pump is operating at a high
    lift, or pumping a large amount of water, using the
    VOLUME position may be necessary to avoid cavitation.
    If high pressure is required (more than 200 psi, 13.8
    bar), operating the pump in the PRESSURE position
    may be necessary even if it means closing one or
    more valves to reduce volume and avoid cavitation.
    The transfer valve may be changed from one position
    to the other while operating the pump. Decreasing
    the discharge pressure will make this easier.
    If the pump has a manually operated transfer valve,
    slow engine speed to reduce the discharge pressure
    to 75 psi (5.2 bar) or less. With the electric transfer
    valve, reducing the discharge pressure is necessary
    only if it exceeds 250 psi (17.3 bar).

    This instruction makes the assumption that the operator has properly set a discharge pressure control device (relief valve or pressure governor).
    Last edited by Johngagemn; 11-04-2009 at 08:06 PM.
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    Disclaimer: The facts and opinions expressed above are mine, and mine alone, and are not intended to represent the views of any company I have ever worked for, past or present.

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    Quote Originally Posted by barnyard2 View Post
    btw...just for your info i am using an older engine where its a manual throttle control
    This is how EVERYONE should learn how to pump. No computers, no electric valves, just plain, old-fashioned "makes you think" kind of pumping.
    "Loyalty Above all Else. Except Honor."

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    Quote Originally Posted by FWDbuff View Post
    This is how EVERYONE should learn how to pump. No computers, no electric valves, just plain, old-fashioned "makes you think" kind of pumping.
    Well said.

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    When i learned to pump we pulled out the parade piece--a 54 lafrance. Evertyhing was manual on that baby. Then we got to work with governors later.

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    Quote Originally Posted by drakescrossing View Post
    When i learned to pump we pulled out the parade piece--a 54 lafrance. Evertyhing was manual on that baby. Then we got to work with governors later.
    I learned on a 1978 Hahn, 2-stage Hale......With Chiefengineer11 breathing down my neck, smacking my hands every time I did something wrong.

    I know when my kids become of driving age, they won't be allowed to drive an automatic until they have mastered a manual.
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    Default I don't know *LOL*

    Quote Originally Posted by chiefengineer11 View Post
    I'd be interested to learn what pump that's on, and how well it works. We had a 1978 Hahn with a Hale QLD pump. The transfer valve was operated by discharge pressure against a piston. It worked well as long as you had 50+ psi greater pressure on the discharge side of the pump than on the intake side. Trouble is, with our monstrous hydrant pressures (185+ on large mains), we rarely had the differntial, so the transfer valve wouldn't operate.

    After fighting with it for years, I finally replumbed it to operate with air rather than water. As an air source I teed into the road to pump shifter, which was air operated. As you mention, it transferred instantly. There was no slow motion involved. I tried putting different orifices in the air supply line to slow it down, but to no avail. It still transferred immediately, or not at all. So I left it alone, and it worked for as long as we had the truck.

    The only thing with it that I never was able to do anything about was that the air had to vent somewhere. Using the Hale valve, there was always a small flow of air from the tank to atmosphere when the pump was engaged. But since the system worked reliably and the air loss was tolerably small, I left it go.

    I wonder how yours is done.
    You know to be quite honest I don't really know how it works. I only tend to figure things out as need be. So far it has worked with no problems hence I havn't tried to fix it.

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    Quote Originally Posted by MColley View Post
    You know to be quite honest I don't really know how it works. I only tend to figure things out as need be. So far it has worked with no problems hence I havn't tried to fix it.
    What pump/apparatus is it on?

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    Quote Originally Posted by FWDbuff View Post
    I learned on a 1978 Hahn, 2-stage Hale......With Chiefengineer11 breathing down my neck, smacking my hands every time I did something wrong.

    I know when my kids become of driving age, they won't be allowed to drive an automatic until they have mastered a manual.
    Good luck finding one by then. You gonna teach them on the FWD? Or will they already have it figured out?

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    Quote Originally Posted by chiefengineer11 View Post
    Good luck finding one by then. You gonna teach them on the FWD? Or will they already have it figured out?
    They may operate the FWD when they demonstrate proficiency with an automotive manual transmission. As far as figuring it out, that reminds me of something I noticed this past sunday. Your eldest grandson would watch as I would shift gears going up and down 309 in Quakertown. I was watching him out of the corner of my eye- when I would shift, he would watch my left leg, and I would see his left leg move in a "press the clutch" motion and he would move his right hand in a "shift the stick" motion.

    I remember watching you shifting the 68 Hahn and listening to the 817G Wauky winding up, and knowing when you would shift by the sound.....So the answer to that is yes, they may very well have it figured out.
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    Quote Originally Posted by chiefengineer11 View Post
    What pump/apparatus is it on?
    It's on an 1981 Thibault Aerial. It's a 1050gpm hale pump.

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    Quote Originally Posted by KuhShise
    Going from series (pressure) to parallel (volume), as FIREMECH states, will lower the discharge pressure (by about 1/2) and might place the attack line in danger if they are using automatic nozzles since it is possible to drop below the 100 psi minimum on the line.
    Anybody care to educate me on automatic nozzles and the 100psi min ???

    FM1
    I'm the one Fire and Rescue calls, when they need to be Rescued.

    Quote Originally Posted by EastKyFF
    "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

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    Quote Originally Posted by FIREMECH1 View Post
    Anybody care to educate me on automatic nozzles and the 100psi min ???

    FM1
    Thats the required minimum pressure (at the nozzle) for most automatic nozzles to function properly.
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    What do you mean by "operate properly"?? The only nozzles I deal with are the deck gun and waterway nozzles. I have no clue what the hand nozzles do, or how they operate (except your basic open/close stream/fog manual type).

    FM1
    I'm the one Fire and Rescue calls, when they need to be Rescued.

    Quote Originally Posted by EastKyFF
    "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

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    An automatic nozzle is designed to always maintain 100 psi nozzle pressure. As you increase or decrease the pressure at the nozzle it will increase or decrease the flow rate through the nozzle in order to maintain the 100 psi. If you drop below 100 psi due to inadequate pump pressure the nozzle performs poorly and you have a very low flow rate.
    Just a guy...

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    Disclaimer: The facts and opinions expressed above are mine, and mine alone, and are not intended to represent the views of any company I have ever worked for, past or present.

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