Gear pump vs. 2 stage splitter pump?

[Justin Erlewine]

Hey guys . New in here but have been following your posts. I have an old splitter that needs some love. The cylinder and the pump are shot. I don't know how to go about rebuilding them due to their are no numbers left on either of them. I happen to have a 21 GPM single stage bi directional pump lying around. The problem with that is from what I have gathered you guys say single stage is not the way to go. Still working on getting another Cylinder and was holding off on that until I know what to do with the pump. Is this pump even worth wasting my time?

 

[sawfun]

Hey guy . New in here but have been following your posts. I have an old splitter that needs some love. The cylinder and the pump are shot. I don't know how to go about rebuilding them due to their are no numbers left on either of them. I happen to have a 21 GPM single stage bi directional pump lying around. The problem with that is from what I have gathered you guys say single stage is not the way to go. Still working on getting another Cylinder and was holding off on that until I know what to do with the pump. Is this pump even worth wasting my time?

If you have enough power single stage requires a lot less oil and stays relatively cool. I have one on my splitter, (not sure of the output) but I'm running a 75 hp 1600cc Pinto engine. It pushes a 5" × 24" cylinder very well. Most splitting is done at 500 rpm with low pressure and 9 seconds. I can gain 3 seconds with more rpm but prefer the quiet low noise of it working at idle.

 

[kevin j]

two stage.
unless very unusual circumstances i would not consider single pump even if free

21 gpm at 3000 psi is about 40 hp.

 

[Justin Erlewine]

The old pump has a pulley system Large drive pulley coming off the motor and small 2.5" on the pump. Why I dont know. Im betting they tried to get more out of the old pump and ended up being its demise. A 21gpm single stage should push about half its potential at about 500-1000rpm shouldnt it? The pulleys basically act like a gear reduction anyway. If I switched the pulleys so the pump is running at lower rpm than the motor puts out do you think it would still be productive?

 

[kevin j]

gear pumps are in the class of fixed displacement pumps. That means they push out a certain fixed flow volume (not pressure) for every revolution of the shaft. It’s typically rated in cubic inches per revolution.
cubic inches per revolution, times the number of revolutions per minute, divided by 231 in.³ per gallon will tell you how many gallons per minute of output flow.

So when it’s 21 gallons pump that has to be specified at some RPM. Then when the RPM and gallons is known the flow is roughly proportional to speed. if you cut the speed in half you’ll have about half of the flow.
the new reduced flow times the pressure will give you a reduced horsepower required to drive pump.

(psi x gpm) / 1714 = hp

and easier to remember rule of thumb that includes inefficiencies things like that is (psi times gallons per minute )divided by 1500 equals horsepower fairly closely.

most pumps are not rated for chain or v belt drive because the tension puts a side load on the front bearing. That’s probably what destroyed your pump eventually. Most pumps are designed for torsional only with the shaft coupling only or they have an optional heavy duty bearing in the front section

 

[kevin j]

also, if you slow the pump down with v belt, the flow drops off. So now you have a 10 gpm (or whatever) pump that still takes 20 hp to drive to full pressure. Way better to have a 28 gpm pump on high speed, then 5 gpm at high pressure, on that same 15-20 hp engine.

might be some issues with driving 20 hp in a v belt, depending on pulley sizexs. Larger pulleys transmit more torque. Might need two belts. then the belt tyension is side overhung load on the bearings again.

If you have to replace cylinder, and pump, I’d look carefully at the engine first, and the beam. Is it worth using the beam and slider, wedge, etc and putting money into it? what size and shape is the engine? What shape and design are the hydr tank, filter, etc?

I would more likely just buy a used 4 inch splitter, typical 5 hp and 11 or 13 gpm pump. Then either run it as is, or if you get impatient with speed, change the cylinder to 3 inch to get serious speed. Search for my post on the 3 inch, 20 stroke, folding splitter. 4.5 hp, 3 seconds out and 3 seconds back.