Circuit!

[keyur trivedi]

hello everybody,
Since last long time i was facing problems of shocks in my machine, during spool transiction of my hydraulic valve. I got so much help by mr. doug, who suggested so many good ideas. After long brain storming i got a very good circuit which can fulfil my requirements without shocks in a single actuater. Though i haven't practically tested yet. I am attaching the circuit herewith. Here i have used 2 no. of(2b2)2-positional valves, which are closed center during transiction, and these are easily available(3c6 are not) in the market. The rest is same in the circuit. Since it's not practically tested, i have few questions to solve before putting it in to my production. It's to be noted that 6 lpm fixed displacement gear pump is used & Pressure compensated 2-port flow control valve is used.
1). Theoriticaly i don't find any trouble, will it work practically?
2). I have fear that once the spool is operated(electrically), it will not come back by spring since the valve is close centered in transiction and pressure is high. Am i guessing right?
3). Should i use check valve after pump? if yes than after pump or after relief valve?
Though i think this circuit will work, i require suggetions from you. You please check the circuit and tell if i can improove it more. Thanks for your attention

keyur trivedi

[Doug Hanson]

The only drawbacks I can see are, the meter out flow control will cause pressure intensification in the rod end of your cylinder. If the cylinder can hande this pressure then there is no problem. It might be better to just a pc flow control as a meter in control and a counterbalnce on the rod side of the cylinder, this may help reduce an initlital 'jump' before the pc flow control has time to throttle back your cylinder. The other draw back to the fixed displacement pump is when you throttle back with a flow control, your pump ends up pumping at relief pressure setting across the relief valve, generating heat.
Your control valve should return to neutral just fine.
A check valve will only be required if your power-unit will shut down while under load, or if there is an external load paced on the cylinder, if that is the case, it's better the check is between the pump and the control valve.

[keyur trivedi]

hello mr. doug,
Finally i have got the way to view the site, through the site u sent in the mail. thanks for your last mail. Now regarding our last discussion. i have few questions.
(1) In our previous discussion we found that closed center will not create any 'jump', then why the 'jump' is there? infact this circuit is to remove 'jumps'
(2) And how the pc flow control in meter-out create pressure intensification?
After a long time i am communicating with the site again. So it's really a good feeling. Thanks!

[Doug Hanson]

Hi Glad your back. The possiblity for pressure intensification exists when you use meter out control on the rod end. If the oil from the cylinder while extending is restricted, this back pressure builds up on the rod side which of course causes the extend side pressure to rise as well, possibly reaching the relief setting of the relief valve. So the extend side pressure will be say 2000 psi and because the area on the extend side of the piston is greater than the net area of the piston on the rod side, you end up with a higher pressure in the rod end. If the ratio of piston areas is 2 to 1 then your rod side pressure becomes 4000 psi.
I don't quite understand your other question. Did you build your circuit as drawn in your last post and it still lunges? The best way I still believe is to use meter in flow control and a counterbalance valve on the rod side.

[keyur trivedi]

hello,
well now i also believe to use meter-in control with c/b. The pressure intensification is a big thing to calculate during meter out. today i understood, and thanks for that! well i will test this circuit wit meter in