I've got a remote controlled double acting HPU that extends the
cylinder slightly after running the retract. What happens is that the
solenoid stops holding the valve before the pump stops running, so a
small amount of fluid goes to the work port.
I imagine this is a pretty common issue. What's the usual solution?
Would a capacitor across the valve solenoid help maybe?
Wrong type of valve for the application. You should have a 'open
center' valve for this application. When the valve returns to center,
the flow from the pump goes to tank, not to any device port. The device
ports are blocked from flow in both directions.
If you have a pressure relief before the valve, after the pump, you can
use a 'closed center' valve. This will also block device ports but it
blocks all flow from the pump when the spool is centered.
"Open Center" valves are typically used with positive displacement pumps.
"Closed Center" valves are typically used with variable displacement
Using a "closed center" valve with a positive displacement pump that runs
continuously will cause all flow to be diverted through the pressure
relief valve when the spool is centered, this is very inefficient and
generates a lot of heat since the pump will be working at the relief
valve pressure setting the entire time the spool is closed. This is the
reason they are typically used only with variable displacement pumps.
You can't 'idiot proof' anything....every time you try, they just make
What is the application? Mobile? Lift gate or hoist? AC or DC?
If it is a double acting system, when you release the button a couple of
things happen. Both
coils on the spool valve should be de-energized, and the power is cut to the
Sounds like the spool valve is not centering properly, or has some damage.
In the relaxed state
the valve should be open from P to T, with the A & B work ports blocked.
It's letting oil
go from T to a work port as the pump winds down. Easy to check.
Disconnect the solenoids
on the spool valve and fire up the pump. If the cylinder moves then it's
time to look at the spool valve. Keep is CLEAN. Disassemble. Look for
physical damage to the spool or bore,
trashed o-rings or seals, broken springs, and crud in itty bitty ports and
It's a DC unit, used with a cylinder on an H-frame press (cylinder is
at the bottom of the frame instead of the top). On this pump, there
is only one valve solenoid. When the up button is pressed on the
remote, the motor solenoid is activated and fluid goes to the work
port. When the down button is pressed, both the motor solenoid and
valve solenoid are activated.
Because the valve solenoid is deactivated almost instantaneously when
the button is released, a bit of fluid is sent out to the work port as
the motor comes to a stop.
On Thu, 09 Nov 2006 01:18:05 GMT, "Andy H. <andys_junk_address at
I think the answer to your problem is to switch the hoses going from
the pump to the cylinder and then change the switch to make it right
again. This will prevent the backing off of the cylinder when pressing
(just make it travel a little bit back down when raising but that
shouldn't hurt much).
Andy H <andys_junk_address at yahoo dot com> wrote:
Is it possible you have air trapped in the system? This would allow
residual pressure to extend the cylinder slightly after the pump had
Does your cylinder have built-in bumpers to cushion the end of the
stroke? Could the bumpers be pushing the piston outward after the
retract pressure is released?
On Sun, 05 Nov 2006 07:31:49 GMT, "Andy H <andys_junk_address at yahoo
Common on the cheaper pumps that just use one solenoid. No real
solution that I know of. My use for the pumps is in hay lifts so I
just make sure that I put the right side of the cylinder to the valve
of the pump to make sure it goes up and stays up properly. A slight
raising back up when all the way down doesn't hurt.
The only suggestions I can think of is to get a different pump (make
sure it has two valve solenoids) or to put add a external solenoid
valve assembly. Both are expensive options.
Or perhaps add a small time delay relay to the coil keeping the retract
solinoid energized for a second (or less?) or so after the original off
cycle to the pump is initiated? This could be relativly inexpensive
and easy to install.
Check out the electronic ones. Adjustable time delay from much
less than one second to 10 hours (going by the example which I picked up
at a hamfest). There is a tiny thumbwheel switch behind the dial plate
(which pops out), and that allows selecting one of ten ranges.
This one was made by "idec" (yes -- all lower case).
Contacts are DPDT, rated at 10A 120 VAC (which should be plenty
for controlling the solenoid), and the "coil" on this one is also 120
VAC, though I'm sure that they have DC voltage ones as well.
It has an octal base, and a knob on the top to select time delay
within the range selected by the hidden thumbwheel switch. The cover
panel has one side marked in seconds and the other side marked in
minutes, and there are slide-ins to change the actual digits displayed
through holes, so the panel can match the range of the selection. The
60 second range is marked off in 5 second increments.
And the octal socket which came with it snaps onto a DIN rail to
join other relays, terminal strips and similar devices.
I have no idea what the new price is (but Mouser probably
carried them). I paid $5.00 at the hamfest, IIRC. Maybe only $3.00.
Email: < firstname.lastname@example.org> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
I imagine there's a timer available for almost every duration and
voltage. In a pinch, however, you might consider just changing the
solinoid coil on your valve (if interchangable) for one with a higher
In addition to the octal plug-in style you can also find "hockey puck"
styles which mount directly to your board.
Andy H <andys_junk_address at yahoo dot com> wrote:
The simplest solution is to split out the switches. One switch
runs the motor, the other controls the valve. When you want to
extend, all is normal. When you want to retract, hit the switch
for the valve first, then hit the motor switch. When you get it
retracted, hold the valve switch, and release the motor switch.
When the motor is fully stopped, release the valve switch.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.