single action cylinder question(s)

[McMXi]

So looking at the schematic below, I'm confused by the suggestion "You can connect the unused port to a tank return (recommended)." For example, if I'm using ports 2a and 3a to control a pair of single acting cylinders, are you suggesting connecting 2b and 3b to a tank return?

 

[Dustball]

This is an easy way to visualize the hydraulic circuit.

-When the spool is moved to the A side, the cylinder extends and the air inside the cylinder is vented through the breather.
-When the spool is moved to the B side, the cylinder retracts and the fluid is returned to the tank for both the fluid coming back from the cylinder and the fluid coming from the pump. Air is drawn back into the cylinder through the breather to prevent a vacuum.
-When the spool is in the center position, the fluid coming from the pump is circulated back to the tank.

For the single acting cylinder, you'll need a breather on the open port and a directional flow control on the connected port so the load doesn't drop like a rock.

 

[TheOldHokie]

I tried to clean up the schematic in the WSM for clarity, but this is the stack of three open center auxiliary hydraulic valves or rear remotes when the levers (valves) are in the center (neutral) position. There are check valves to prevent flow back towards the pump.

View attachment 149231

Here's the flow when a valve is activated, let's call it position 1.

View attachment 149232

Here's the flow when the valve is activated in the opposite direction.

View attachment 149233

There is no questuon the main PRV will unload at max system pressure. If it did not normal operstions woild fry the pump in short order. The PRV in the loader valve will do the same.

My point was and is you can prevent the system from unloading through the PRV with a simple tank return.

Dan

 

[TheOldHokie]

This is an easy way to visualize the hydraulic circuit.

-When the spool is moved to the A side, the cylinder extends and the air inside the cylinder is vented through the breather.
-When the spool is moved to the B side, the cylinder retracts and the fluid is returned to the tank for both the fluid coming back from the cylinder and the fluid coming from the pump. Air is drawn back into the cylinder through the rklfts breather to prevent a vacuum.

Depends on the cylinder design. A true displacement type SA cylinder has no internal seal,only one port, and dies not have a brearher. Different animal than a DA cylinder being used in a SA application.

They are inexpensive, trouble free, and have been used on agricultural equipment for better part of a century Common examples are snow plow angling and forklift mast cylinders.

Dan