questions/clarifications

[sitnbakwrds]

Hello all. I'm a first time poster and I have a few questions regarding some pump operations. I'm preparing to start practicing some pumping on our drills and I need a little help. I used the search function to try and find some answers but had little luck finding the answers I needed. So, if these are repeat questions I apologize in advance.

First, my understanding is to leave the tank to pump valve open even when you have an established water supply. This way, in the event you loose your supply, you wouldn't have to hurry and open the tank to pump valve so hoseline crews would not have any loss of water. Is this correct? It seems to me some engineers close their tank to pump valves when their tanks are full so they know if they loose their supply they have a full tank for firefighting operations.

Also, with respect to the tank to pump valve I believe our trucks our clappered so when there is a supply coming into the truck the water pressure from the supply closes the clapper valve sothe pump is fed by supplied water and not from the tank. Does this sound right? I know there are various valves and different kinds of pumps in use so whatever thoughts you have would be welcomed.

Second, I'm in Arizona so the temperatures here can be particilarly hot. I've noticed most engineers keep the tank valve "cracked" so the water in the tank is constantly moving (recirculating) to prevent the water from reaching extreme temperatures. This seems logical to me but I'd like some other opinions.

Finally, does anybody know of any websites that can be used to reference formulas, pump operations, etc? If so, let me know.

Thanks in advance for your help.

[chiefengineer11]

My personal practice is to keep the tank to pump valve closed. In most cases it doesn't hurt to leave it open. But if you draft, you need to remember to close it, or you'll be drafting the tank. Like any other valve (or any part of the pump,for that matter), if it isn't used, it won't work when you need it to. Depending on water quality, you get a build up of deposits that can chew up the valve seals in pretty short order. Operating them frequently keeps that stuff wiped off.

Clappers, or check valves are or should be in place to prevent backflow into the tank, but I'm not sure that I trust all of them.

Keeping water flowing is important with any pump. It's super critical with single stage pumps. You can actually boil standing (in the pump) water in no time. You can even boil tank water. The smaller the tank and the hotter the weather, the greater the risk. If you get Chief Billy Goldfeder's "Secret List," there's an item about a three firefighters receiving scald burns just recently. One of them had to be admitted to the hospital. I don't think he mentioned the pump, but I'll bet it was a single stage. It's just one among several reasons that we continue to run two stage pumps. (But I have to admit, it could have been a two stage pump left in volume.)

Most pumps today are equipped with circulator lines, but in my opinion and experience, they're too small. They're usually 3/8" or 1/2" lines. And, they have a valve on them. This is one valve that I leave open most of the time. So yes, it's a good practice to crack open the tank fill valve to keep water flowing. This should be one of the very first things you do after putting the pump in gear. It doesn't matter where you are. In cold country, you do it to keep the water from freezing. Get water moving, keep it moving!

Stay safe out there, everyone goes home!

[Chauffeur6]

I agree with the above post, but just to clarify one thing: ANY pump will cavitate at some point, no matter what type it is (midship, rearmount, frontmount, PTO, etc) or how many stages it is or what mode it's left in (volume or pressure). You leave the same water in it for enough time while the impeller(s) are spinning, and eventually the pump will heat it up enough to possibly cause damage. I've seen it happen with a large Waterous dual stage CMU midship pump left in pressure in the DEAD OF WINTER, so just imagine the potential in 100+ degree ambient temperature!

Keep those tank discharge and tank fill valves open anytime you're sitting idle to avoid damage. What that does, in effect, is use the entire tank as a giant radiator to keep the pump cool. It's not so much an issue while you're actively flowing water, especially when using an external water source (hydrant, drafting), but it's always something you need to be aware of.

[chiefengineer11]

6, you're absolutely correct that any pump can overheat and cavitate. We train our drivers, first thing after putting engaging the pump, get out and start circulating water. If you stop flowing and it looks like you won't flow any for a while, just put the main trans into neutral (doesn't apply to PTO drive and front mounts).

The tank certainly does function as a big radiator, but I've seen cases where people have even overheated them while circulating. Worst case conditions: Operating from tank, small tank, hot weather, single stage pump, maintaining hand line pressure, no or minimal flow from the lines.

MG3610's thread about circulating water quotes the article that Billy G cited and that I referred to in my last post.

Philadelphia Fire Department has used two stage pumps for many years. They do now have a few single stage. I was talking to the driver of E16, which at the time was a Freightliner E1 and had a one. I asked him what he thought of the single stage. He replied, "I guess it's OK if you like hot water from your discharges."

Stay safe out there, everyone goes home!

[BirkenVogt]

Cavitation is not the correct term here, it is a much overused word. Cavitation is what happens when you over-pump your supply. A different form of it can also happen when sitting idle with one of these monster 2000 GPM pumps. But in this case the pump simply overheats the water. They make automatic bleeders with flashing lights you can mount on the pump panel to inform the operator of this.

Sometimes I use the fire pump as an "engine dyno" when I am working on a fire engine. I open the tank to pump and tank filler wide, set the relief valve at 150, and throttle up until the engine is running at its 150 flow rating (1250 in my case) RPM. This way I am running the engine at full load while stationary and can look for problems without having to go on a road trip, etc. It is interesting to see how quickly the tank water heats up in that situation! You are basically dumping close to full rated engine HP into the tank water in that situation. At least 200 HP worth if not 250. That's 500-650 k BTU/h

Birken

[FWDbuff]

The Chief Engineer is obviously suffering from old-age dimentia, and has forgotten to mention one of the most important things related to circulating water- COLD WEATHER.

Very, very important to circulate water, not only in hot weather (to assist the engine cooling system) but also in cold weather, to prevent the pump and assiciated piping, valves, etc from freezing.

[Chauffeur6]

Cavitation is not the correct term here, it is a much overused word. Cavitation is what happens when you over-pump your supply. A different form of it can also happen when sitting idle with one of these monster 2000 GPM pumps. But in this case the pump simply overheats the water.

You just contradicted yourself. First you say cavitation is NOT the correct term, then the very next sentence you say that the boiling water IS a form of cavitation. I don't mean to pick nits, but the simple fact is that in the broad sense of the term, cavitation refers to the formation of vapor bubbles in a liquid. This can be achieved by either a low pressure/high speed situation OR result from the liquid boiling. Saying "it's what happens when you over-pump your supply" is oversimplifying it.

[Chauffeur6]

The Chief Engineer is obviously suffering from old-age dimentia, and has forgotten to mention one of the most important things related to circulating water- COLD WEATHER.

Very, very important to circulate water, not only in hot weather (to assist the engine cooling system) but also in cold weather, to prevent the pump and assiciated piping, valves, etc from freezing.

...

So yes, it's a good practice to crack open the tank fill valve to keep water flowing. This should be one of the very first things you do after putting the pump in gear. It doesn't matter where you are. In cold country, you do it to keep the water from freezing. Get water moving, keep it moving!

[chiefengineer11]

Thanks, 6. You saved me from having to do it. Young son reads well, writes better and is a truly "good jake." But occasionally he does tend to gloss over stuff. And reticence, especially as a critic, has never been one of his attributes. If it involves me, so much the better.

Stay safe out there, everyone goes home!

[Weruj1]

I think everyone needs to slow down and READ posts before replying .........we recirculate water if not activley flowing any, no matter what the ambient temperature is.

[npfd801]

For anyone (not the posters here, for sure) that doesn't think that the water heats up, check out the UL test pits at any of the rig builders. 16,000 gallon underground tanks (for example) are heated into the 90 degree range doing pump tests for UL, to the point that much of the water needs to be replaced as it doesn't cool enough daily to continually do UL pump tests without elevated water source temps.

Recirculating water is always a good choice, but if I'm on a hydrant and know I won't be flowing much water, I'll crack a discharge and constantly flow some water to keep the pump cool. Obviously, this can be bad in winter, as you only create a slick spot next to the rig.

One of our newer engines has a bleeder that dumps the pump water if it gets too hot, another engineer tripped it once, and it doesn't go unnoticed. He thought he blew the truck up, as it was pretty cold out when it occurred, and the rig was instantly enveloped in a very large cloud of steam. Everyone else noticed as well... As with everything that happens in the fire service that was a mistake, do you think he's heard the end of it?

[chiefengineer11]

Cavitation is not the correct term here, it is a much overused word. Cavitation is what happens when you over-pump your supply. A different form of it can also happen when sitting idle with one of these monster 2000 GPM pumps. But in this case the pump simply overheats the water. They make automatic bleeders with flashing lights you can mount on the pump panel to inform the operator of this.

Sometimes I use the fire pump as an "engine dyno" when I am working on a fire engine. I open the tank to pump and tank filler wide, set the relief valve at 150, and throttle up until the engine is running at its 150 flow rating (1250 in my case) RPM. This way I am running the engine at full load while stationary and can look for problems without having to go on a road trip, etc. It is interesting to see how quickly the tank water heats up in that situation! You are basically dumping close to full rated engine HP into the tank water in that situation. At least 200 HP worth if not 250. That's 500-650 k BTU/h

Birken

My first inclination was to agree with you on cavitation, Birken. Cavitation certainly does occur under the conditions that you describe. The physics of it, as I learned it many years ago is that as we pressurize a liquid (water, in this case), we raise its boiling temperature. Similarly, as we go into negative pressure (drafting, for example), we reduce the boiling temperature. When we are attempting to pump more water than can be move through our hard sleeves, we also have brought the water below its reduced boiling temperature. Some of that water begins to form drops containing steam, which, as they contact the pump's impellers, implode (explode?) with considerable force. That, in turn, causes serious physical damage to the impellers. Sorry, my explanation may not be clearly stated, but it's my understanding of the physics involved.

Where I question both your version and Chauffer6's (he alludes to your own statement) is this: As we heat up standing or slowly moving water in the pump case as happens when the pump is turning against no or minimal flow, does the same phenomenon occur?

I'm not at all certain but would like to hear from someone with a better understanding of the physics. What I am certain of is that either situation will put us inside anyone's any model pump, replacing some very pricey parts.

One other question, Birk. Are you certain that you can move 1250 gpm through your tank-to-pump and your tank fill lines? That seems to me to be quite a lot. What size are those lines? I'm accustomed to seeing 3, 3-1/2 and sometimes 4" tank-to-pump and anywhere from 1" up to 1-1/2" internal fill lines. Even as short as they are, I'd be surprised to see that much, or anything even close to it. Even if I fill our engines from a 185 psi hydrant (yes, we do have that, on 20 and 22" mains to boot) going in a pony inlet or the steamer, it takes a couple of minutes to fill a 500 gallon tank.

Even if you can, are your engines developing their maximum horsepower in order to move that amount of water?

I'm not trying to snipe at you, I'm trying to learn. The stuff you put in here and I read tells me that anyone, even someone as old as I am can learn from you. The same applies to many other contributors here.

Stay safe out there, everyone goes home!

[fpvfd502]

To keep it simple and prevent problems:

Don't keep the tank to pump valve open unless you want water from the tank. Having to pay attention and open valves in a hurry is not a valid excuse for leaving it open. Most all pumps are clappered with a brass flap...but its not safe to assume it seals perfectly.

Idle down and recirculate when not flowing lines. Its takes effort. If engineers are not willing to do this...don't let them operate. Go to neutral if your going to be sitting for a while. Recirculate in cold weather too. If your connected to a hydrant...stick a section of hose on a side discharge and route the water elsewhere. Or simply idle down and overflow the tank until you get tired of water everywhere.

Just don't keep 200 psi on the master gauge and flow nothing. Pumps need to pump somewhere. Feel the water coming from a dischage to tell how warm your getting if your worried.

On Saturday night...I was accepting 5" supply in relay from a pumper drafting form a 6 tanker shuttle. I was pumping to an aerial master stream and a ground monitor. I did this for 6 hours solid in a commercial downtown fire. There was alot of switching from booster tank to supply etc...and idling down and kicking into neutral based on the needs of the folks I was supplying and my supply. We were able to keep the master streams going continuous except for a couple 10 minute delays in the shuttle (railroaded).

It aint easy...but its what to do.