Can someone explain this circuit?

[rfc143]

This is from a brand new single acting hydraulic pump, probably Chinese. Documentation really sucks. It works perfectly; i.e. up button turns on pump; down button opens another valve to lower the dump body. But the circuit makes no sense to me. I can see the pump, and check valve. I believe A is a pressure relief valve, and B is the load holding valve which opens when it comes down, but what are C and D?

 

[WranglerX]

Maybe.....

Hydraulic Symbols

 

[ptsg]

This is from a brand new single acting hydraulic pump, probably Chinese. Documentation really sucks. It works perfectly; i.e. up button turns on pump; down button opens another valve to lower the dump body. But the circuit makes no sense to me. I can see the pump, and check valve. I believe A is a pressure relief valve, and B is the load holding valve which opens when it comes down, but what are C and D?

Since this is a dump body:

A - Pressure relief valve
B - Solenoid valve to lift/lower the bed.
C - Flow restrictor so the bed comes down in a controller manner, otherwise it would small very fast and very hard.
D - Manual ball valve to manually lower the bed in case the solenoid fails.

 

[BigGG]

A is a relief valve
C and D appear to be manual valves. They may be there to manipulate the raising and lowering speed?

 

[rfc143]

Since this is a dump body:

A - Pressure relief valve
B - Solenoid valve to lift/lower the bed.
C - Flow restrictor so the bed comes down in a controller manner, otherwise it would small very fast and very hard.
D - Manual ball valve to manually lower the bed in case the solenoid fails.

I'll go with you on C: I've identified a variable flow adjustor that can adjust the down speed. It's the wrong symbol for an adjustable valve, but let's not quibble.
As for D: there is no manual ball valve anywhere to be found. Perhaps some models have it; some don't? Good idea though.

 

[ptsg]

I'll go with you on C: I've identified a variable flow adjustor that can adjust the down speed. It's the wrong symbol for an adjustable valve, but let's not quibble.
As for D: there is no manual ball valve anywhere to be found. Perhaps some models have it; some don't? Good idea though.

The manual valve may not be a regular ball valve but a cartridge valve on the block that one would push, pull or twist somehow to let the bed come down.

 

[LD1]

Since this is a dump body:

A - Pressure relief valve
B - Solenoid valve to lift/lower the bed.
C - Flow restrictor so the bed comes down in a controller manner, otherwise it would small very fast and very hard.
D - Manual ball valve to manually lower the bed in case the solenoid fails.

Agree 100%