Re: Re: Re: GPM rating of the Cub hydraulic pump?

Posted by Andy Martin on February 15, 2001 at 14:07:48 from (38.31.75.63):

In Reply to: Re: Re: GPM rating of the Cub hydraulic pump? posted by Mat on February 14, 2001 at 22:06:02:

Sorry, a sheave is a pulley for a v-belt. Pulley usually refers to a flat or crowned pulley. Sheave is the proper industrial term for single or multiple v-belt drives.

What I was trying to say is that you can pick the pulley (sheave) diameter to make the pump turn the speed necessary to put out the flow you want. Even an 11 gpm pump is OK if it is turned slowly by putting a large sheave on it.

A power steering pump will probably work, but you will likely need a larger reservoir, both to fill the cylinders and for cooling. Pick out the pump you want, and turn it by hand to measure the ounces per revolution it will pump into a measuring cup (use your wife's best one, leave it in the shop full of oil, and make sure the pump is pumping pure oil (no air) to get a good test). You may want to turn it 10 or 20 revolutions to get enough oil to measure accurately. Divide by the number of turns to get how many ounces it pumps per revolution.

Then figure out the pump's speed. Look at the engine it came off to determine how fast the pump turns compared to the engine: divide the harmonic balancer diameter by the pump sheave diameter to find the speed multiplier. A 4-inch sheave on the pump with a 6-inch harmonic balancer will make the pump turn 6 divided by 4 or 1.5 times as fast as the engine. Estimate the truck engine speed to determine the pump maximum speed. Probably 5,000 rpm for a gas engine and 3,000 for a diesel. So if it is a diesel truck, the pump will safely turn at 4,500 rpm, and probably much more. Since you know how much oil the pump will put out in one revolution, multiply that by the pump speed to get ounces per minute, and divide by 128 to get gpm. For example, if the pump put out 3.5 ounces in ten revolutions, that is .35 ounces/rev. For 4,500 rpm, that is 1575 ounces per minute. Or 12.3 gpm. If you want 4 gpm, turn the pump at 1/3 speed, in this example, 1,500 rpm, or about the engine speed for an A.

BUT you have to measure the pump you pick out and do the calculations! The pump will put a little less out under pressure and at speed than your hand test, so overspeed it a little from what you calculate, that is why I picked 4 gpm for the example.

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• Re: Re: Re: Re: GPM rating of the Cub hydraulic pump? mat 18:58:08 02/15/01 (0)

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