open center/ closed center
open center/ closed center
(OP)
When using a closed center valve what is the normal practice used to keep pressure off pump when valves are in center posistion? Doing no work.
I used air to check if fluid would circulate through the valve when spools are in center posistion. No circulation which leads me to beleive the pump would be under a High load when doing no work.
Using a Husco 5000 series double action motor valve in tandem and wish to controll 2 motors in forward, reverse and one forward while the other in reverse. Like in a zero turn mower. Built this thing from scratch. Only a fool like me would do this. I have a million hours in it and enough $ to buy a cheap one. Don't recomend anyone to build your owne. I understand fluid circuts untill I get to the question above. Thanks.
I used air to check if fluid would circulate through the valve when spools are in center posistion. No circulation which leads me to beleive the pump would be under a High load when doing no work.
Using a Husco 5000 series double action motor valve in tandem and wish to controll 2 motors in forward, reverse and one forward while the other in reverse. Like in a zero turn mower. Built this thing from scratch. Only a fool like me would do this. I have a million hours in it and enough $ to buy a cheap one. Don't recomend anyone to build your owne. I understand fluid circuts untill I get to the question above. Thanks.





RE: open center/ closed center
Ted
RE: open center/ closed center
Mike Halloran
Pembroke Pines, FL, USA
RE: open center/ closed center
It can also be used with a fixed displacement pump if there is a load sensing unloading valve (externally or in the valve inlet section) but it requires a load sense signal from each of the spool sections. Essentially, that load sense signal controls the unloading of the pump when work is or is not being done. If it is not already in the valve stack I think you would be better off getting a new valve. To convert the spools, or add external load sense shuttles, is beyond the normal back yard skills.
If the valve is commonly available and not obsolete, you might be able to get open center cylinder or motor spools and convert the spools only, without trying to add load sensing. Check with the rep for the valve brand and part numbers.
Changing to variable pump may be possible, but the control and heat generation under most operation at light loads make this a less desireable way to go IMO.
kcj
RE: open center/ closed center
RE: open center/ closed center
Thanks again.
RE: open center/ closed center
Mike Halloran
Pembroke Pines, FL, USA
RE: open center/ closed center
Ted
RE: open center/ closed center
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: open center/ closed center
Mike described the center of spool condition.
Open center descibes the P & T connection only. A & B connections are separate terms. It can have blocked work ports A&B (usually called cylinder spools) that hold position, or can have AB connected to P & T (motor spools) that float.
You should be able to exchange the spools to open center, but it may get pricey.
+1 on the cooler, no restrictions on the suction side. Typically put a 50 psi or so check/releif valve around the cooler so if ther are surges or at cold start the maximum pressure is limited.
ed, I think the sun numbers for check and unloading valves require an accumulator circuit to store energy and unload the gear pump. without an accumualtor they would short cycle or chatter on and off, ormaybe act as a stright relief valve converting all the flow to heat.
kcj
RE: open center/ closed center
You are correct, an unloader circuit with a gear pump must have an accumulator. This type of system is best for functions that cycle from high flow to no flow.
For a wheel drive steering system you need a tandem center spool for each wheel. This will create more heat than a hydrostatic pump and motor an each wheel but will be less expensive.
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: open center/ closed center
After reading all the input I will redesign the drive system (the whole system). As of now I am designing around parts I can get at surplus center which is overstocks, takeoffs, and discontinued, most are new and the prices seem good. There descriptions are such I can understand. I have looked for a real hydraulic supply house online and they all seem incomplete. I will explain new design.
I have calculated using motors I have (6.2cu in CHAR-LYNN 104-1062) that 10gpm (5 to each) will speed with tire size to almost 14 mph which is plenty enough speed. Starting at the tank to pump(0.73cu in gear pump) (through suction filter) than to a pair (in parallel) of motor speed (flow) controls (pressure compensated) with adjustable relief then sending controlled flow to a electric reversing valve, sending un-used flow to 4 way joystick (for mower deck to up/down and side to side movement) then back to tank through cooler. (Bypass around cooler with pressure valve good idea jck) Electric reversing valve will forward and reverse drive motors. Steering accomplished by varying speed controls. Zero turn by reversing one or the other reversing valves. Going to do all the steering and drive with foot pedal and steering wheel, can't be the same as all the rest of zero turn mowers out there.
What are the things to look for as far as this circuit is concerned? I find hydraulics is likened to a combination of plumbing and electronics. Accumulators/capacitor, flow valve/potentiometer and must be considered.
This board is great, thanks again.
Louisville,Ky
RE: open center/ closed center
- Kirchoff's Laws apply, but the resistors are nonlinear.
- you can get killed in different ways.
Mike Halloran
Pembroke Pines, FL, USA
RE: open center/ closed center
Always put the cooler in the return line before the filter.
The cooler will generally handle more back pressure than the filter will.
RE: open center/ closed center
Ted