Re: Re: Re: PTO HYD PUMP PREBLEMS?

Posted by How Hydraulics Works!...T_Bone on January 02, 2001 at 00:56:55 from (207.254.53.43):

In Reply to: Re: Re: PTO HYD PUMP PREBLEMS? posted by todd on January 01, 2001 at 20:35:49:

Hi Todd, You can't have a pump thats continously pumps under high pressure with no return or you'll burn the pump seals up because of the heat.

With a one-way valve with closed center the pressure will continue to build to pump maxmium output. If you add a two-way check valve, the flow would be from the pump to a tee on the in-put side of the spool valve, the 90* part of the tee would also supply pressure to the #2 in-port on the check valve at the same time, then the #2 out-port of the check valve would go to the cylinder return port (the rod end), as soon as the return stroke was complete then the #2 in-port on the check valve would go maxmium pressure and the relief (check) would open returning fluid to the tank from the #2 return-port on the check valve. Now lets open the one-way spool valve to split a log, the flow would be from the spool valve to the #1 in-port of the check valve, then from the #1 out-port of the check valve to the cylinder in-port thus moving the ram out too maximum stroke, then the spool valve would close forcing the pressure back thru the 90* on the tee thus starting the cycle all over.

No we don't plumb hydraulic systems this way but I thought it would give you an idea of how a one-way spool valve cycle could work.

Now lets look at a two-way spool valve closed center with a releif valve(check valve). Pressure from the pump would goto the in-port on the spool valve, then the out-port of the power stroke port on the spool valve would go to the in-port of the cylinder, the spool valve would then be pulled sending pressure to the cylinder an would travel maxmium stroke splitting the log or lifting the bucket, then the spool valve lever would return to center with ram being at maxmium stroke, then the spool valve lever would pushed sending pressure from the pushed out-port to the in-port on the rod end of the cylinder returning the rod to minmium stroke. If the spool valve was left in the center closed position then the pressure would open the return releif valve(check valve) on the spool valve thus returning fluid to the tank.

Now lets look at a open center two-way spool valve. Pressure from the pump would go to the in-port of the spool valve and return to the tank thru the return out-port of spool valve, hence a fluid flow loop without a relief valve. Now pull the spool valve lever and the pressure would flow from out of the pulled out-port of the spool valve to the cylinder in-port thus splitting the log or raising the bucket at maxmium stroke and blocking flow to the return port, then the spool valve lever would return to center sending the fluid back to the fluid flow loop, then we push the spool valve lever blocking flow to the return out-port and sending pressure to the cylinder in-port at the rod end returning the rod too minmium stroke, then the lever would too center putting the system into a another fluid flow loop.

Now if we had a open center one-way spool valve with releif valve, then pressure would flow from the pump to the in-port of the spool valve and building pressure on the relief valve, then as soon as the pressure reached relief valve pressure setting then fluid flow would return to the tank thru the spool valve return out-port. When the spool valve lever was pulled, pressure would be sent from the spool valve out-port to the cylinder in-port extending the rod to maxmium stroke, then the fluid from the rod end of the cylinder would return to the spool valve return in-port thus putting pressure on the relief valve to the set pressure thus returning fluid to the tank. When the spool valve lever was released, then pressure would flow to the rod end in-port reutrning the rod too minmium stroke and continue building pump pressure until the relief valve opened sending fluid back to the tank.

This is just basic systems that could work and maybe will give someone a better understanding of a typical hydraulic system.

T_Bone

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