Sizing Motor to Hydraulic Pump

[lsloth]

Picked up a pump today that I hope will work with my 2.5" bore 24" stroke, 2500 psi ram that I picked up a couple of weeks ago for my Pro-tools conversion. I am little confused on what size motor I need to run the pump to work well with my ram. Here are the specs I have found. I think I need a 5-7.5hp motor but that just sounds high. What do you guys think? It’s a Vickers Piston Pump, model PVB5-FLSY-20-C-11.

Here are the specs at 1500rpms:

http://www.r65.org/pump/1500rpm.jpg

Here are the specs at 1800rpms:
http://www.r65.org/pump/1800rpm.jpg

Does this chart mean the pump must have at least 15psi on the inlet for the pump to work?

http://www.r65.org/pump/inletpressure.jpg

Thank you for helping this hydraulic newbie.
-James

[jasonmt]

Rule of thumb:
Horsepower=(GPMxPSI)/(1714xEfficency)

So if you want 3 GPM@2500psi(g):

HP=(3GPMx2500psi(g))/(1714x0.80Efficency)
HP=7500/1371.2
HP=5.5 with 5HP being the closest motor.
You would want to spin the pump at ~1050RPM to ensure that you had no problems with overworking your motor which would entail a flow of ~2.75GPM @ 2500psi

5 GPM @ 2500 psi would require ~9.12HP and the pump spinning at 1900RPM which is over speeding the pump, at the 1800 RPM max speed you are looking at ~4.75GPM of flow.

As the energy input from the power source is going to be a static number you can play with the variables of flow and pressure (energy output less losses due to friction, seal leakage etc.) to attain a combination that will suit your intended use and power source. The same 5HP motor that will get you 2.75GPM @ 2500psi when spun at ~1050 RPM OR 3.92GPM @ 1750psi when spun at ~1500RPM.

Note that Absolute Pressure what is referenced on the chart, the Absolute Pressure of the atmosphere at STP as defined by IUPAC is 14.696 psia or 0 psig so the ~15psia as the minimum inlet pressure on the chart is the pressure exerted by the atmosphere.

[jasonmt]

I feel a few more comments must be made here as well as piston hydraulic pumps generally have poor overall efficiency as well as a low rpm range when compared to other styles but are capable of the highest pressures.

I would be more inclined to design a smaller system such as this around a smaller displacement gear style pump that can have much higher overall efficiencies (95% for some gear pumps versus 80% for the piston) as well as higher RPM ranges.

A gear pump that is 95% efficient with a displacement of .231 cu. in. and a maximum speed of 4500RPM will match up great with a 5HP 3400RPM motor and allow it to be direct driven. With this setup you are looking at 3.23GPM @ 2500 psi compared to the 2.75GPM from the same 5HP driving the above piston pump. The smaller gear pumps usually have fairly high maximum pressure with the .231 cu in model having a maximum pressure of 3150psi.

Similarly a .129 cu in displacement pump is a good match for a 3HP/3400 RPM motor and will provide 1.9GPM @ 2500 psi and require 2.9HP to run.

[lsloth]

Thank you very much for your input, I only paid 12 bucks for the pump so I do not feel to bad about it. I think I will keep my eyes peeled for gear pump, 5+hp motors are pretty pricey and I have not had good luck finding them used around here. On a side note this pump can spin up 3600rpms according to the tech sheet.

[jasonmt]

The price sounds right depending on if it is new or used. It is unfortunate that it is a larger displacement pump that makes it somewhat unsuited for your use. Another problem would be that I doubt that it is designed for side loads on the input shaft which makes adjusting the input speed from the motor a more complicated affair that simply throwing on a set a sheaves/sprockets and a belt/chain.

If you look on page A5 of the spec sheet you will find that the variable displacement pumps (PVB*) are limited to 1800RPM, the fixed displacement models (PFB*) are able to go to 3600RPM with the proper fluid usage.