RPM for Hydraulic Pump

What do you think will happen if you run a positive displacement pump at 1/2 speed?

You must have some idea.

These people may be able to help.

http://www.dynexhydraulics.com/index.htm

UK distributor at the bottom. It's probably best to get an 1800 rpm pump.

http://www.dynexhydraulics.com/distrib.htm

Seems to me you should just purchase a 1800 rpm pump and live with whatever efficiency it gives you. If you already possessed a 3600 rpm pump then a speed increasing transmission would probably be a good idea. If your 14 HP engine was already connected to a generator then a 3600 rpm electric motor seems practical.

Hi

Tell me where in the Uk you are situated and I'll give you a source for your pump. Someone who knows what they are doing. You will need the full details of the engine including the various shaft outlets such as crankshaft and camshaft

Oliver Dunthorne

Hydraulic Engineer

Thanks, I am in Co Down in Northern Ireland. The engine is a Petters AVA2 which used to run a wood saw.

If a 3600 rpm (positive displacement) pump is run at 1800 rpm, theoretically it should give half the through-put. But practically it won't, due to internal slip. Slip is a factor of clearance area and the differential pressure (discharge - suction). This slip would be the same for any speed. Actually at higher speeds, the slip could be lesser due relatively faster moving gear tooth tips would try to drag the back flow at a faster rate than the slower speeds. So it is advisable to run the pump at the designed speed.

For raising the speed, installation cost pulley arrangement could be cheaper than gear box, but not so considering the maintenance cost as well.

The issue arises because you have already taken a decision to use a hi-lo pump, which is a unit consisting of 2 gear pumps and a valve.

First of all, these type of pumps run fine at 1800 rpm. In my opinion it's below 600 rpm that's an issue.

If you want pumps rated for 1800 rpm, you should look for industrial application pumps and/or truck pto mounted pumps. But you will likely not find any hi-lo pumps.

Gears are ready available. In some cases the pump manufactures offer the gears. Using belt and pulleys is also an option.

My experience with UK is that there's plenty of supply both for new and secondhand equipment. And normally people from mainland Europe doesn't have any issue sending the parts you need either.

What type of motor do you have that runs at 1800 rpm?Is it gasoline or diesel?1800 rpm seems very slow for a standard gasoline motor.It may have been governed down to this speed for a particular application.Normally,most small hp engines such as yours are rated at 3600 rpm.If this is the case,a simple adjustment of the speed governor (Regulator)would allow you to bring your speed up to desired value.

Some small diesel engines are governed down for durability purposes,and I would not increase the speed unless I was willing to sacrifice longevity of the engine.

IF your motor is electric(improbable,but possible),the RPM change of the motor itself will be expensive, requiring a rewind of the motor.

I will hazard a guess that the application is a log splitter, and you want a hi-low pump to decrease cycle time of the ram?

If this is the case, let me know, I have some suggestions before you get too much $ invested in this project.

BTDT(Been There, Done That)

3600 rpm rating is usually the max rpm. Most pump manufactures list performance at 3600 and 1800 rpm. Which are the common electric motor rpm. Even as other have said 1800 rpm on a gas motor is low. Most likely has been govern to match an electric motor so they can offer both electric and gas. Keeping specs the same.

The 1800 rpm still isn't a problem you just need to match the displacement of the pump at that rpm to the rate you need the cylinder to move. In increasing the displacement you will also need to take into account the hp rating. The manufacture will usually have a recommend hp rating on the pump.

Ok, to start with some basic engineering, you have enough HP to provide roughly 9.5 Gallons/per minute at 2500 PSI.

You will need at least a 10 gallon reservoir and good filtering of the hydraulic fluid.Vegetable based hydraulic oil is now available that will not pollute ground water if it leaks.(Never seen a system that did not leak a little bit after some serious work).

Your cylinder requires approximately 1.3 gallons to achieve full stroke on piston side of cylinder.

At 2500 psi,it will provide approximately 6 complete stroke cycles per minute.The return stroke will be a little faster, due to the displacement by the output shaft.

A 10 second cycle is pretty good for a log splitter, if this is the intended purpose.

I don't see a need for a 2 stage pump unless you are performing this work on a production line or piece-count basis.

A very important factor to consider is the anchoring of all components of the system to prevent misalignment of the moving components.The cylinder is vulnerable to side thrust, which will quickly destroy seals and bushings.

The ram should travel on support rails as far as possible,with an appropriate pivot to allow slight changes in misalignment that will occur under load.

2500 psi applied to a 4 inch diameter cylinder will produce over 30,000 pounds of thrust, so do not under-engineer the framework.Also look carefully at the output shaft diameter of the cylinder, to make sure it can handle the load imposed.

My favorite design for a log splitter is an H shape,like a hydraulic press.Very strong,very stable.(And people cannot borrow it for a full season. )

I would put a throttle control on the motor to allow for varying conditions.Some wood is very hard to split.

A PTO Rated pump should work well for your application,and many are available with a simple google search.

Good luck

Feedback from the OP is always appreciated,and will ensure a sincere effort from respondents on the next question the OP might have.

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Merry Christmas to all of you Christians out there.

Happy Holidays, as appropriate, to all others.

Feedback from the OP is always appreciated,and will ensure a sincere effort from respondents on the next question the OP might have. Yes sorry I have been away with work for a while and only got back last night. Where I was no Internet has ever existed, in fact we came home when the batteries ran out :-) I have had a chance to read your informative post and will take on board the advice. The H design is interesting, I have plans for a horizontal (and yes it is a log splitter app). I am in Northern Ireland. The engine I have is a old fuel Petters AVA2 which is rated at 14hp at 1800rpm, no gear box is involved. Before anyone comments :-) I have three of these machines all fully restored and as I have them already I want them put to work. The idea is to mount the lot on a trailer. Yes I could buy a new engine but where is the fun in that. Another option I have is to make a mount for my Smalley 425 grave digger and use the PTO, again a lot of work but that is what fills in the winter months in the shop.