Hydraulic help needed

[oldnslo]

In reading the specs on the valve Port 1 is not intended as pressure port.

 

[LouNY]

OK, from the hydraforce website;
A solenoid operated, two position, three way, direct acting spool valve. When de-energized, the SV12-
34X allows flow from port 2 to port 1, while blocking flow at port 3. When energized, the spool shifts to
open from port 3 to port 2 while blocking port 1. While port 1 may be fully pressurized, it is not intended
to be used as an inlet

So port #2 as the pump or pressure port,
port#3 as the cylinder port,
and port#1 as the return to tank
and adding a check valve before port #2

a copy of the pdf from Hydraforce;

 

[oldnslo]

OK, from the hydraforce website;
A solenoid operated, two position, three way, direct acting spool valve. When de-energized, the SV12-
34X allows flow from port 2 to port 1, while blocking flow at port 3. When energized, the spool shifts to
open from port 3 to port 2 while blocking port 1. While port 1 may be fully pressurized, it is not intended
to be used as an inlet

So port #2 as the pump or pressure port,
port#3 as the cylinder port,
and port#1 as the return to tank
and adding a check valve before port #2

a copy of the pdf from Hydraforce;

Lou,
how do you get the cylinder to lower now? Port 3 is never connected to tank.

This valve could work if he teed it into the cylinder port and installed a check valve between the pump and tee. Plumb the 3 way with cylinder to port 3 and tank port 2. Port one 1 would not be used. He also needs a system relief between the pump and check.

 

[LouNY]

OK, from the hydraforce website;
A solenoid operated, two position, three way, direct acting spool valve. When de-energized, the SV12-
34X allows flow from port 2 to port 1, while blocking flow at port 3. When energized, the spool shifts to
open from port 3 to port 2 while blocking port 1. While port 1 may be fully pressurized, it is not intended
to be used as an inlet

So port #3 as the pump or pressure port,
port#2 as the cylinder port,
and port#1 as the return to tank
and adding a check valve before port #2

a copy of the pdf from Hydraforce;

Whoops;
corrected the port numbering above.

so supply to port #3
cylinder to port#2
return to tank port #1
With a check valve before the input of port#3
With the pump running and the valve energized flow would be port #3 to port #2,
with a check valve prior to port #3 with the pump shut off the system should hold in that position,
after time the pump could be bumped on to repressurize the system or increase the pressure to further stroke the cylinder,
when the valve is de-energized the fluid will return to tank allowing the cylinder to retract.

 

[oldnslo]

Lou,
agree that the corrected porting would work.

 

[r8f1k]

So I have the following:

Port 1: to pump
Port 2: to cylinder
Port 3: to tank though a filter

Now what do I need to buy?

 

[LouNY]

So I have the following:

Port 1: to pump
Port 2: to cylinder
Port 3: to tank though a filter

Now what do I need to buy?

nope, follow the below

so supply from the pump to a check valve then to port #3
cylinder to port#2
return to tank from port #1 thru your filter
Add a check valve before the input of port#3
With the pump running and the valve energized flow would be port #3 to port #2,
with a check valve prior to port #3 with the pump shut off the system should hold in that position,
after some time the pump could be bumped on to repressurize the system or increase the pressure to further stroke the cylinder,
when the valve is de-energized the fluid will return to tank allowing the cylinder to retract.

 

[r8f1k]

Recommendations for a check valve?

 

[oldnslo]

Recommendations for a check valve?

Any check rated for pump flow and pressure should work

I doubt that you can put a filter in tank line for lower since pressure drop through the filter could prevent the press from opening.

I recall another post on similar sounding system where we calculated there was less than 10 PSI to open the empty press and seal friction was causing his press to not open fully. A 10 inch bore is 78.54 square inches so 10 PSI will lift 785 lbs.

 

[etpm]

So I have the following:

Port 1: to pump
Port 2: to cylinder
Port 3: to tank though a filter

Now what do I need to buy?

You need a check valve between the pump and the cylinder. I am not the first person to tell you this. The check valve should really be right after the pump and before anything else. The reason for this valve is because the pump design will not allow it to hold pressure. This is because of the way a vane pump works. The rotating part of the vane pump has slots in it that hold the vanes. This rotating part is off center to the bore of the pump. As this rotating part rotates the vanes will be contacting the bore. Since it is off center the vanes must move in and out of the slots. Of course they don't come all of the way out of the slots. The vanes must maintain a fairly tight fit against the bore in order to seal against the bore and deliver the fluid being pumped at the desired pressure. Usually this tight enough fit is accomplished by the vanes being forced against the bore by centrifugal force. This of course requires the pump to be spinning. So when the pump is stationary it will not seal very well, hence the inability to hold pressure and the need for a check valve. I hope this helps you understand better what is happening with your system and why you need a check valve.
Eric