Trash pump, vs High pressure fire pump?

[Skeans]

We have both a trash pump tank and one with a high pressure pump to be legal, the trash pump is mainly used to washing equipment well on the jobs. Seems like the fire pump with a 25 horse Honda was around a grand a few years ago.


Sent from my iPhone using Tapatalk

 

[HuskStihl]

Uh, Jon? If you gave me a medical opinion I'd recognize the experience, education, and training behind your adice and I'd probably do exactly what you said. Not knowing as much as you do I'd be foolish to argue with you.
If 2Dogs gave me advice on fire related stuff I'd treat his advice the same way as I'd treat yours.

Not even remotely questioning the honorable 2-dogs' fire-fighting knowledge and advice, merely wondering about northy's needs. I know nothing about fahr's, but am quite expert at running a small business (and thus somewhat protective of fellow small business owners) and diligently containing costs. If Northy doesn't need a $2k pump, he shouldn't buy one. If I was mistaken, and he is intending on being a fire fighter, then by all means get the pump which will overcome long hose runs and elevation changes

 

[Gologit]

Not even remotely questioning the honorable 2-dogs' fire-fighting knowledge and advice, merely wondering about northy's needs. I know nothing about fahr's, but am quite expert at running a small business (and thus somewhat protective of fellow small business owners) and diligently containing costs. If Northy doesn't need a $2k pump, he shouldn't buy one. If I was mistaken, and he is intending on being a fire fighter, then by all means get the pump which will overcome long hose runs and elevation changes

True, a guy doesn't want to spend unnecessary money. Man, I sure understand that.
But when buying fire equipment the cost difference between "might work" and "will work" is all you're really spending. When you're dealing with something that might save your life or the lives of others a few extra dollars shouldn't be a consideration.
Whenever we bought pumps we'd always get something just a little larger and more powerful than we thought we might need. When the time came to use them...and it always did eventually...we were very glad to have the extra power.

 

[2dogs]

If the intent is to have a fire trailer pump, the pressure required is in The Timber Sale Contract. You might want to visit your Darrington ranger station for requirements.

Despite my lengthy post slowp's advice is really the best. Find out in writing what the requirements are.

 

[northmanlogging]

If the intent is to have a fire trailer pump, the pressure required is in The Timber Sale Contract. You might want to visit your Darrington ranger station for requirements.

Well that pretty much settles it then, I doubt that the FS is going to be ok with a cobbled together hunk of scrap (unless I paint it first). And I'm almost certain the pressure rating is going to be more then the 40psi I could "maybe" squeeze out of a trash pump...

So for know I'll save my pennies and hold out until I find a either a used fire pump for the right price, or get one of the northy tools honda's for around $800.

I'm currently not working FS or DNR ground, so its a want more then a need... But I have gotten some invitations to bid, (to big for this dummy)... So in reality a cobbled together pump would be better then nothing... but it does need to work, and work correctly.

Thanks again gang! and welcome back Ms.P

 

[BeatCJ]

Edit: My post was based on my misunderstanding. I apologize for the way I started it. The last paragraph can probably stand on it's own, though.

Northy how can I say this politely...uhm most everything written here is wrong. No offense guys but this was my profession for many years.

I know it's not the intention, but I am offended. I know, I've only been doing this for 27 years, so what I am saying does have some room for error. I have built (plumbed on tanks I spec'ed) 2 slide in units, one survived many inspections on federal fires. It is still in use, but we make more sending out Type 5's with 400 gallons and keeping the Type 6 at home. It's on it's third chassis, now. Since it wears brakes less with 1600 lbs less water, and even this time of year we run about 75-80% EMS calls, we're OK with that.

Spending the money on a "Fire" pump is great, if you have access to the budget. But many less expensive pumps will meet the expressed needs. The way I read it, he's looking for something to catch his mistakes quickly. Decent flow, decent pressure from most pumps will do the job. Minimalist plumbing, a single length of 1"hose and he can be fine.

That said, if it's contract requirements, then slowp's answer is best. I gotta say, the cobbled together crap I see some of the guys using around here as a "fire trailer" makes you wonder why they don't start more fires. I think even they wonder if they will start, if they really need them.

Rant off, I feel so much better.

 

[Hddnis]

http://www.amazon.com/Emergency-Fir...pebp=1440209189842&perid=1MYGXS3Y5QZ98MX6WBMY

I've got one of these getting shipped to me right now. One of my Honda powered pumps sucked a rock and broke the impeller, we need to get that skid unit back up and going so we're going to try this pump out.

This is another option I considered, looks like basically the same pump.a
http://www.carrollstream.com/1_1_2_inch_High_Pressure_Water_Pump_p/40zb60-4.8qt.htm

I've build a few units that have cast iron Hypro centrifugal pumps, with a v-belt speed increaser. They go to 130psi and move at least 100gpm using Briggs 9hp motors.

On trash pumps...
Good volume, no pressure.
Some of the water transfer pumps do alright. I've got one that makes about 46psi and it will hold its own as a fire pump on level ground with shorter hoses. But once you add in a hill and 200'+ feet of hose it really falls off performance wise.



Mr. HE

 

[catbuster]

I still stand behind the smaller the hose you run at a specific GPM the more pressure and throw you get at the nozzle. The velocity of the water increases. F=MA. Physics and stuff, you know? It won't change the pressure at the pump. I'm a newbie by your standards at 11 years of this. I did, however, get an engineering degree along the way, which means oodles and oodles of dynamic physics classes... But you even said that in your post. I think you misinterpreted what we were all saying.

 

[northmanlogging]

Bugged the local saw shop guys, they can order a transfer pump that runs 50 psi at 3", and something like 250 gpm, only runs like $500 with a honda motor. Choke it down to 1.5" hose and a fire nozzle on the end a 270 gallon tote might last more then 3 minutes... Or split it to tw0 2 1" lines...

This may be the route I end up going.

Seriously though same pump on C's list $800?

 

[2dogs]

I still stand behind the smaller the hose you run at a specific GPM the more pressure and throw you get at the nozzle. The velocity of the water increases. F=MA. Physics and stuff, you know? It won't change the pressure at the pump. I'm a newbie by your standards at 11 years of this. I did, however, get an engineering degree along the way, which means oodles and oodles of dynamic physics classes... But you even said that in your post. I think you misinterpreted what we were all saying.

You can not get any more pressure than what the pump is rated for by decreasing the diameter of the hose. You have to understand how a centrifugal pump works. The impellor spins inside the curved pump housing even when water is not flowing. This is called 100% slippage. (The opposite type pump where water must flow is called a positive displacement pump). The maximum pressure developed is here in the volute and decreases further from the pump, i.e. as the discharge hose is lengthened (on level ground) due to friction loss. An example might be the pump has a 1 1/2" discharge flowing at 50 psi at the pump. You put a 1/4" smooth bore nozzle on the end of 100' of 1 1/2" hose. The pressure will never exceed 50 psi at the nozzle. Changing the hose to 1" diameter can not increase the nozzle pressure above 50psi. Any pump Northy buys will have a pressure/volume chart. As the pressure goes up the volume goes down.

Fire pumps are expensive because the tolerances are minimal and the pump has to be durable. Still, you can get a decent portable pump for $1,500.00 or a bit less. (I like spending other peoples money). Substituting an inexpensive general purpose pump or a slightly more expensive trash pump for a rated fire pump may give the user a false sense of security at best or set him up for a disaster at worst. Like slowp said "Trust but verify". I think she said that anyway.

 

[2dogs]

Bugged the local saw shop guys, they can order a transfer pump that runs 50 psi at 3", and something like 250 gpm, only runs like $500 with a honda motor. Choke it down to 1.5" hose and a fire nozzle on the end a 270 gallon tote might last more then 3 minutes... Or split it to tw0 2 1" lines...

This may be the route I end up going.

Seriously though same pump on C's list $800?

Northman if you buy a wildland nozzle, that is a dual gallonage aluminum nozzle designed for firefghting, it will usually be 60 GPM on the high setting and 20 GPM on the low setting. This is at 100 psi nozzle pressure. It is likely you will be flowing 20-40 GPM with a small pump on the high setting and 100' of hose. If you buy an inexpensive plastic nozzle if will be a single gallonage type and will flow around 20-30 GPM but with a poor quality stream. It is what you will find on most water buffalos and should work OK for your use.

 

[catbuster]

You can not get any more pressure than what the pump is rated for by decreasing the diameter of the hose. You have to understand how a centrifugal pump works. The impellor spins inside the curved pump housing even when water is not flowing. This is called 100% slippage. (The opposite type pump where water must flow is called a positive displacement pump). The maximum pressure developed is here in the volute and decreases further from the pump, i.e. as the discharge hose is lengthened (on level ground) due to friction loss. An example might be the pump has a 1 1/2" discharge flowing at 50 psi at the pump. You put a 1/4" smooth bore nozzle on the end of 100' of 1 1/2" hose. The pressure will never exceed 50 psi at the nozzle. Changing the hose to 1" diameter can not increase the nozzle pressure above 50psi. Any pump Northy buys will have a pressure/volume chart. As the pressure goes up the volume goes down.

Fire pumps are expensive because the tolerances are minimal and the pump has to be durable. Still, you can get a decent portable pump for $1,500.00 or a bit less. (I like spending other peoples money). Substituting an inexpensive general purpose pump or a slightly more expensive trash pump for a rated fire pump may give the user a false sense of security at best or set him up for a disaster at worst. Like slowp said "Trust but verify". I think she said that anyway.

I understand centrifugal pumps. I've torn enough of them down and rebuilt them to grasp that. But the thing is, the physics there aren't even happening at the pump.

It's physically impossible to keep the pressure the same if the velocity of the water increases. It's that simple. You're not increasing pressure at the pump, you are simply increasing the velocity of the water to keep the GPM the same, which makes the pressure go up. Pressure is a force, you convert volume to mass and the acceleration cannot remain the same. It's pretty simple. The nozzle may not allow it, but the physics behind it are sound, not that theoretical fluid dynamics matter at all to this discussion.

 

[2dogs]

I understand centrifugal pumps. I've torn enough of them down and rebuilt them to grasp that. But the thing is, the physics there aren't even happening at the pump.

It's physically impossible to keep the pressure the same if the velocity of the water increases. It's that simple. You're not increasing pressure at the pump, you are simply increasing the velocity of the water to keep the GPM the same, which makes the pressure go up. Pressure is a force, you convert volume to mass and the acceleration cannot remain the same. It's pretty simple. The nozzle may not allow it, but the physics behind it are sound, not that theoretical fluid dynamics matter at all to this discussion.

That is not the way it works. If you attempt to reduce the diameter of the discharge hose but keep the same discharge volume then the pressure has to be increased. You can not do this without increasing the pump's "power". This can not be done with the type of portable pump we are talking about. (It is like saying that you can take a small cheap Chinese made Husky chainsaw and put on a four foot bar and an 8 tooth sprocket and go fall trees with it. The power just isn't there to turn that big heavy chain. Getting the chain up to speed might be possible but as soon as contact is made with the wood then the chain slows down too much to cut and the clutch starts to slip).

The difference of course is that the portable pump runs flat out all the time and the pressure/volume relationship is charted at full throttle. In a liquid the pressure is the same in all locations measured. This means pressure readings are taken with water flowing and no elevation change. The only real variables have to do with friction/appliance loss. Yes in theory slight changes can occur in certain circumstances, read venturi, but then velocity increases and pressure goes down. In simpler terms more "force" can not be applied to the water by a portable pump. Think about the fire engine you work on. You probably have an engineer's pump chart, aka a cheat sheet, somewhere the engineer can look at a 03:00 when his brain is only half awake. If he needs more volume then he cranks up the rpm and the pressure relief valve and adjusts his discharge gates as needed. In other words he applies more "force" by burning more fuel.

 

[hanniedog]

Northman check out gov surplus in your area for used fire equipment.

 

[Marshy]

Sounds to me like you need to know what the requirements are for the build. You need to answer what is the minimum GPM, PSI and length if hose you will use? You will also need to know the maximum elevation difference you will use the hose relative to the pump.

Once you answer the above questions you can do some basic math and figure out the size of your pump. When looking at pumps you should look at the performance curve of the pump. It will tell you what the discharge pressure will be developed at a certain GPM. That same curve will also tell you what the required HP is and most importantly, require net positive suction head NPSHr (inlet pressure).

Everything in the first paragraph needs to be known to build a proper system. If you build a system incorrectly and size it wrong it might work right on flat ground but not at all if you drag a 100' hose up a 25% grade.

Of course you could just oversize everything if you do not know the engineering side of it. That is completely acceptable to some people, the downside is the added cost I buying equipment you don't really need. That's a personal call.

 

[northmanlogging]

Ok so what I can figure out here, and what I was originally not assuming is that given a certain amount of flow and head, you can increase pressure by decreasing hose/nozzle size. I get this from the old gold dredging method of piping water down hill and necking it down, no pumps involved. The unrelenting force of gravity being the power generator. This method works because there is usually a large pond or catch basin several hundred feet above where the water jet is stationed, several hundred feet of water in a large enough pipe, hooked to the bottom of a pond could potentially be hundreds of pounds of pressure.

With a centrifugal pump, and this is the guts of the original question, the force is supplied by making the water move through faking gravity. But since said pump can only turn so fast, and it will have necessary clearances for the use in questionable water, the finale pressure can only be what the pump can handle at the pump. Necking it down does not work since any extra pressure gets lost in the clearance of the pump, by not allowing more water to come through the inlet only so much can leave the pump at one time. Ultimately you are limited by how much water the pump can move through whatever line you intend to use, necking it down will only cause you to use less water per minute, which is a good thing in the end. Also velocity will not change, being that pressure has to increase to increase the velocity... its a catch 22.

So the question now...

Is 50 psi enough to use up to 200' of hose, at 25% slope up hill? This would be the absolute extreme use of said pump, any more then that and hopefully the fire dept is on there way...

 

[2dogs]

Slope is calculated as rise over run. Therefore .25 equals X over 200, X equals 50'. A 3 in 12 roof has a slope of 25%.

So water flowing uphill will have to overcome head pressure. This is 1/2 psi per foot of elevation gained. In addition water flowing through a hose will suffer friction loss due to the roughness of the hose. The standard calc for 1 1/2" hose at 60 gpm and 100 psi nozzle pressure is 13 psi per 100'. In your case let's just say your friction loss will be 5 psi per 100'.

So starting with 50 psi at the pump let's deduct friction loss , 2X5, or a 10 psi loss. Now your nozzle pressure is 40 psi. Ok so let's take the nozzle up the slope till we run out of hose. We have walked uphill 200' and have gained 50' of elevation. Head pressure has robbed us of .5 X 50 or 25 psi more. Now you are down to 15 psi at the nozzle. I am guessing here but that will probably result in the nozzle throwing water about 15 feet. So nope, a 50 psi pump won't work in this case

 

[Hddnis]

I'll just wade in again to say that 2dogs is right on all this stuff.

The post above mine where he works it out to 15psi at the nozzle is a great example of why fire pumps can make higher pressure, they have to be able to do it just to get the water where it is needed with usable pressure.

Velocity in the hose can only come from pressure at the pump. You simply can't use a smaller hose and get more throw from a nozzle. There is no equation or "physics stuff" out there where that works, period. Higher velocity out of a hose without a nozzle can be achieved with a smaller hose, up to the limit of the pump. But once you put a nozzle on the end the smaller hose immediately starts to work against you, because the velocity is generated by the compression of the nozzle acting on the flow of water.

Bottom line as I see it is: A "low pressure" pump is better than a bucket, but for practical use more pressure is better. I personally consider 125psi a minimum for fire protection. I've seen specs where 200psi was the minimum on contracts and others that simply refer to forest service specs.

So that brings us to wildland engine specs.

Lowest rating I could find said 8gpm at 65psi. Others say 10gpm at 100psi for a type 7 engine.

https://en.wikipedia.org/wiki/Wildland_fire_engine

http://www.nps.gov/fire/wildland-fire/learning-center/fire-in-depth/engines.cfm

http://www.fs.fed.us/eng/pubs/pdf/00511203.pdf



Mr. HE

 

[BeatCJ]

If he is dragging 200', it's most likely not 1 1/2", more likely 1". So friction loss will be significantly more, at 30 gpm, 23psi per 100'.

I know, he's a bull, but 1 1/2" hose is best charged after it's laid out.

Northy, let me know, I can probably set you up with 300' of old USFS 1" hose and a couple of red plastic nozzles. It's been stored inside, but I would plan on only getting a season or two out of it. Still, it would be something you wouldn't have to buy right now. It's 1" NPSH thread (like pipe thread but not tapered, black gas line thread).

Do your saw shop guys have access to the pump curve? Most times, as flow decreases, pressure rises. So at 50 psi, that pump is flowing 250 gpm (all numbers pulled from my posterior, generalized, not necessarily accurate). But, at fire flow, 40 - 50 gpm in your case, the pump may be capable of 150 psi. For you, that would give you about 75 psi at the nozzle. Not quite desirable, but it would work. Most fire nozzles are designed to give optimum pattern at 100 psi nozzle pressure.

 

[northmanlogging]

Ya better hang on to that hose for now... might need it this year, though I wouldn't turn it down, I could probably get a lot more then 2 seasons out of an old hose... (get yer mind out of the gutter)