Hydraulic driven pumps

[Catch22]

I had a potential monetary donor throw a question out to me yesterday, thought I'd throw it out to you guys. This guys started going on about the gas-powered pumps we all use on our brush rigs and how his trucks he uses to spread chicken waste use hydraulic-driven pumps. Basically, he asked me why we didn't use them on our brush trucks.

Any of you guys ever hear of anyone using this kind of pump? Any idea where to even start to look for one if a guy wanted to consider it?

The reason I ask is he may be able to be talked into buying us a brush truck. If it's an affordable option, I may look into it.

[firepiper1]

What he is most likely referring to is a PTO driven pump. Most pump manufacturers offer them. My dept has never used one, so I can't give you too many details.

[SBrooks]

Just a few thoughts, nothing real to back them up. At one time I was an engineer, but haven't been in practice for a while, and never as a mechanical engineer.

Usually hydraulic transmission of power from a motor to an implement is done for one of three reasons: the first is for flexibility, implements can be changed out fairly easily, farm implements, hydraulic rescue tools, etc.; the second is that there is a convoluted path from the motor to the implement such as in hydraulically driven wheels on some off-road construction & agricultural vehicles; thirdly is when the speed of the implement must change in relation to the motor speed, such as in some hydralic generators. One problem with hydralic transmission is that it's not very efficient, all the friction loss in the piping etc. robs engine power to the implement. This is why you see big radiators on most constant speed hydraulics such as generators. The friction is converted to heat which must be removed by airflow over a radiator. In low flow push pull piston operations this isn't nearly as important - for hydraulic pistons on rescue tools or construction equipment, the fluid reservoir and/or hoses are usually sufficient for cooling.

Where such factors are less important, it's usually far more efficient to mechanically couple (as opposed to fluid couple) the motor to the implement. So usually, a fire pump has a midship transfer or a mechanical pto arrangement. For a small pump brush truck, the power requirements are such that a standard pickup truck motor has more than enough power to be able to 'afford' a fluid coupling but.... the preponderence of evidence is such that a separate small motor with a direct mechanical coupling is the cheaper / easier way to go, at least for small pump applications. For larger designed flows, a PTO pump is used, and a compromise between desired pump speed and desired wheel speed is made.

Note, here are your typical fire pump options:
"PTO" pump
Diesel or gas motor > road transmission > pto > water pump
Slip in unit, some ARFF trucks
(separate) Diesel or gas motor > water pump
Standard fire engine
Diesel or gas motor > road transmission > transfer case > water pump
Hydraulic pump system
Diesel or gas motor > road transmission > pto > hydraulic pump > piping > hydraulic motor > water pump

Note that the hydraulic system has a few more complexities that probably aren't necessary for a dedicated brush truck.

Just a few thoughts, and I readily admit I may be quite wide from the mark.

[GreggGeske]

SBrooks does a great job of explaining the power transmitting possibilities for the fire pump. The big reason that hydraulic driven units are not used on brush trucks is cost. It is about one third the cost for a 18HP direct engine driven pump than to set up a system to be hydraulically driven. There are quite a few applications that due use hydraulically driven pumps (CDF for example) and all the pump manufacturers offer hydraulic drive options on the pump. Some applications do not offer a clear path for the transmission PTO to pump, so a PTO and hydraulic pump can be faced to the front and then the hoses routed to a hydraulic motor mounted on the water pump.

[canuck1]

high pressure

I know of a "Brush Type" truck that does use a hydraulic pump. The truck actually has 2 pumps on it. One "Volume" pump, which they use for tank filling (gasoline engine), and one "Pressure" pump (hydraulically driven), which they use for fire fighting operations. They need the pressure pump because sometimes they will have very long up hill hose lays, and they still want lots of pressure at the tip. The hydraulic pump was the only small sized pump that could provide the kind of pressure they wanted ( I think it was like 400 psi)

[neiowa]

What is a brush truck? 150gal w/18hp baby pump or a real wildland truck with large tank and pump.

The chicken poop spreader likley uses a hydraulic driven pump for the same reason "better" (and more expensive) offroad/wildland trucks use a hyraulic driven pump. That is eliminates the surges/variable pressure/flow that you will have with a PTO driven pump due to changes in engine rpm caused by operator and terrain as you drive cross country. A hyraulic system with a pump (PTO or direct from engine) suppling fluid to to hyraulic motor driving the water pump eliminates this problem. The hydraulic pump evens out the power "flow". Can also run a large pump (up to structural size). The Lexus (formerly Cadillac) solution.

The seperate engine driven baby pump is pretty much the Yugo solution (but due to $ what we have on our truck as well). Cheap to buy but that's about the best you can say about it.

If you're driving a large spreader truck across a field spreading smelling stuff I'll bet same problem. You want a uniform distribution and a hyraulic spreader would be the likely solution.

With some creativity you could economically put together a hyraulic system using DOD surplus or ebay equipment.

He's buying sign him up.

[BirkenVogt]

I disagree with the hydraulic being the end-all be-all. CDF has some it's true but they are universally hated and they are old and on the way out. I really, really like our 3-cylinder Daihatsu Waterous aux pump on our main engine, it is nice. It will power several hand lines and that is all you need off it really. The engine also has a full 1250 main pump. The hydraulic pump is going to have way more maintenance issues and control issues than a separate aux pump.

Birken

[Catch22]

I think you guys answered most of what I was wondering. The biggest thing was a functional and cost issue. I've never come close to pricing a hydraulic driven pump, and only used them in the farm setting.

NEIowa--Just to clarify, I was talking small brush truck. Maybe something with a little heavier chassis and more water, but nothing huge by any means.