BradK,
There are two basic types of hydraulic systems. They are open center and closed center. Most tractors, probably all small, use the open center type.
The differances are:
Open center -series circuit-fixed displacement pump.
Fluid supplied from the pump is allowed to flow through the valve unrestricted back to the reservior (tank)when it is not being used to do any work. =0 system pressure.
When a function is actuated such as extend a cylinder or turn a motor the spool in use diverts the oil flow from returning to tank to the desired function. While doing this pressure is built by the resistance of the load until the relief pressure is reached. =System pressure setting. At this time the relief cartridge dumps oil to tank until the pressure is below its setting.
There are two basic variations on this type, with or without a (P.B.) power beyond (some times called high pressure carry over).
Without a power beyond there are only two lines besides those going to functions. The pressure line from the pump and a return line to the tank. The return line not only carries oil that is not being used for a function but also oil that is venting on the low pressure side of a double acting function.
With a power beyond there are three lines besides those for functions. Pressure line from pump, return that only carries low pressure returning oil and the power beyond.
Power beyond is that "tap" that we all need when we want to add more valves. The power beyond prevents the high pressure from building up on the low press. (return) that causes all the problems from not using one. Leaks, spool binding, warped housings, overheating and such when a down stream valve is actuated.
Numerous valves can be put in series as long as all but the last valve is using a power beyond.
pump to loader valve inlet, p.b. to second valve inlet, p.b. to third valve inlet and so on. All valves will have a return to tank. last valve no p.b.
Closed center -load sense-parallel circuit-variable displacement pump (briefly) pump and all valves are connected by a sense line. When Valves are not actuated there is what is called rest pressure. Rest pressure drops off as a function is used. The pump then puts out more oil pressure or volume until rest pressure is back to normal or system pressure is reached. It is a much more expensive, complicated system that has much lower tolarence level for dirt and untrained service procedures.
Thers is my Hydraulics 101. /forums/images/graemlins/smile.gif
There are two basic types of hydraulic systems. They are open center and closed center. Most tractors, probably all small, use the open center type.
The differances are:
Open center -series circuit-fixed displacement pump.
Fluid supplied from the pump is allowed to flow through the valve unrestricted back to the reservior (tank)when it is not being used to do any work. =0 system pressure.
When a function is actuated such as extend a cylinder or turn a motor the spool in use diverts the oil flow from returning to tank to the desired function. While doing this pressure is built by the resistance of the load until the relief pressure is reached. =System pressure setting. At this time the relief cartridge dumps oil to tank until the pressure is below its setting.
There are two basic variations on this type, with or without a (P.B.) power beyond (some times called high pressure carry over).
Without a power beyond there are only two lines besides those going to functions. The pressure line from the pump and a return line to the tank. The return line not only carries oil that is not being used for a function but also oil that is venting on the low pressure side of a double acting function.
With a power beyond there are three lines besides those for functions. Pressure line from pump, return that only carries low pressure returning oil and the power beyond.
Power beyond is that "tap" that we all need when we want to add more valves. The power beyond prevents the high pressure from building up on the low press. (return) that causes all the problems from not using one. Leaks, spool binding, warped housings, overheating and such when a down stream valve is actuated.
Numerous valves can be put in series as long as all but the last valve is using a power beyond.
pump to loader valve inlet, p.b. to second valve inlet, p.b. to third valve inlet and so on. All valves will have a return to tank. last valve no p.b.
Closed center -load sense-parallel circuit-variable displacement pump (briefly) pump and all valves are connected by a sense line. When Valves are not actuated there is what is called rest pressure. Rest pressure drops off as a function is used. The pump then puts out more oil pressure or volume until rest pressure is back to normal or system pressure is reached. It is a much more expensive, complicated system that has much lower tolarence level for dirt and untrained service procedures.
Thers is my Hydraulics 101. /forums/images/graemlins/smile.gif
