Greetings from a newbie to this forum.

I collect and restore Colt and Case garden tractors and these machines use a simple hydraulic drive system.

Most tractors utilize a standard two hole mount gear pump in either A or AA form with GPM ratings from 7.5 to 9.5 at 3000 RPM. The flow of these pumps is directed through an open-center control valve with a built-in relief and that valve supplies oil to a geroller style of drive motor bolted into a 2-speed transaxle.

From the control valve, the oil returns to the reservoir after passing through a cooler for the next go-round.

I'd like to have the ability to test pumps on tractors I am restoring so that I know I am not putting a bad pump in. It was my intention to take one of the old tractors and use most of the hydraulic components plus the Kohler K engine and make up a simple flow bench.

I would replumb the system to allow the flow meter to be installed between the pump output and the control valve plus I would Tee in a pressure guage at this spot too. The control valve's ports would be plugged in order to create the pressure in the system.

Have I got this right or am I totally off-base here? Thanks in advance.

Tom

I trust the Tank port is hooked to Tank ALSO.

With an Open Center Valve (P to T) the flow meter should show full pump flow anytime it is running.

When you shift the valve and the flow to tank is blocked all pump flow must go over the Relief Valve ar whatever presure it is set for.

If the pump is good, flow will continue at a reduced rate but should be 85-90% of what it is rated at and/or is delivering while it unloaded to tank.

This test will only be viable when th pump is at operating temperature. If the pump is good and the oil is not bad there should be no apprecaible drop in flow from Cold Oil to Operating Temperature Oil.

Listen for a change in pump NOISE as pressure builds. If te Pump Inlet line has a problem and is restricting flow te pump will get louder as pressure builds.

The open center control valve has six ports in total because it has two spools and each spool has its own relief valve.

To make sure that we are on the same page, that double spool valve has an inlet for oil coming directly from the pump. It also has an outlet that is plumbed directly to an oil cooler and that is plumbed to the reservoir. There is no "power beyond port" or any other port

The other four ports relate to the spools. On spool normally would control a small hydraulic cylinder (2 1/2" D. X 5" stroke} that is used to raise and lower implements such as the mower deck and snowblower. The relief for it is set at about 500 PSI.

The other spool is what we refer to as the "Travel Valve" because its two ports are connected to the Geroller motor that drives the tractor in forward and reverse. Tractor speed is also metered by this valve. It's relief is often set at about 2100 PSI.

So, the system is very basic. Pump to control valve to oil cooler to reservoir and back to the pump. All I wish to do is introduce a Flow Meter between the pump and the valve so I can test the pump's output under varying conditions. The oil normally used in Colt/Case/Ingersoll tractors is 15W40 or 20W50 and Shell's Rotella T diesel motor oil is a preferred brand.

Plumb the Flow Meter in the Pump Linet and then to the valve inlet. You will see flow when the pump is running and the valves are in Neutral.

Plug all 4 Workig Ports so pump flow cannot go anywhere except to Tank, Free Flow or across a Relief Valve.

rom the explanation you give the valve for the drive motor will have to be shifted all the way to completely block flow and send it all over the Relief.

Thank you very much, Bud. I thought that I was on the right path with this little project but I just wanted to be sure. It's always cheaper to do it right the first time around. LOL

While I haven't had one of those "travel valves" apart, I'm sure that the spool is tapered so as to gradually increase the volume of flow to the motor ports. So, in order to achieve the pressures that will tax the pump to the limit, I will have to push or pull that valve to the limit so that all of the flow is forced past the relief.

I don't know if there is anything further to be said on any aspect of my proposal, as it appears that Bud has already answered my questions. However, if anyone else has something to add, please feel free to do so.

Thanks again.
Tom