surging!!

[keyur trivedi]

Hello experts,
I have made a power unit for wood packing drilling cycle. I used meter out pressure compansated flow control for that. Since cycle is wood packing, whole stroke of cylinder is not under feed. Only cutting stroke is under feed and rest of the travel is done by rapid. So during forward stroke as it change over from rapid to feed, the surge occurs. And in return as it change feed to rapid, the surge again occurs. That surge may be because of higher pressure drop at flow control valve which may cause excessive flow for a while. As mr. doug guieded me previously. Now can i use a counter balance valve in order to remove that surge? Will it work? Or some other change is req. to be done? During meter out surge is usual or it depends on bore to rod dia. ratio? Should i change my circuits from meter out to meter in? Waiting for your reply.

Regards,

Keyur v. Trivedi

[Doug Hanson]

Hello keyur. Do you have a schematic that you can post, to make sure we are talking about the same things? If the load on your cylinder varies, a counter balance valve will help out. If the surging is a result of the sytem, it might not be the solution. Some caution needs to be used with meter out on the rod side of the cylinder while extending as pressure intensification may result. That is the draw back, but it usually provides for a more stable control.
If you use a counterbalance valve on the cylinder, while rapid feeding under no load, the CBV will generate heat and waste energy. If you can draw and post a schematic that would be great.

[keyur trivedi]

Hello mr. doug,
Thanks for your reply and guidance. You are very helpful to juniors or newcomers like me in the field of hydraulics. And yes here with i have attached circuit drawing of my system. As you can see system is very simple. Now valve-1 which is for clamping creating no problem. Problem is there in between valve 2 & 3. All the directional valves are p-t types. relief valve setting 50 bar. Now cylinder you can see is horizontal. During it's extension stroke half of the stroke is cutted in rapid motion, and rest is cutted by flow controlled motion. And during it's return again same thing happend. Function of directionsl valve 3 is to provide flow control valve in line when ever necessary.valve 2 drives the cylinder. Now during extention stroke(fluid enters from bore side and leaves form rod side) when ever valve 3 starts to convert rapid motion in to feed motion, the surge occurs. Or when ever the push button is operated the jump or surge occurs. It causes excessive noise and the jumping can easily damage the drill. Diameter of bore is 63 mm and rod dia. is 40mm. Once you told me that bore to rod diameter ratio can create surge. Is there any formula for that? or how it affects? Pressure is 50 bar pump capacity 8 lpm. So now can i use counter balance valve attached with outcoming line of cylinder, or meter in circuit is must for this? I am really cofused about these jumps or surges. It usually occurs ever time i make power system. Problem is i don't know the proper reason behind it and the sollution also. Is it because i use meter out flow control every time for my system? Should i use meter in with counter balance next time? I am in favour of meter out always but these surges make me confused. So plz guide me through this, waiting for your reply.

Regared,

keyur trivedi

[Doug Hanson]

Is this the same machine that you were working on before, that was a clamping, boring, drilling machine?
The problem might be the 'transition state' of the control valve. Some times the transition is all ports blocked, sometimes is is all ports open, which in this case might be allowing a momentary increase of flow, especially with the cylinder control valve shifting while the meter out control is creating back pressure. In the transition state, the control valve will allow oil to both sides of the cylinder, which will cause it to lunge in a regenerative state.
Can you do one more thing for me? Can you state which brand and model number for the flow control and flow control's directional control valve, and cylinders control valve?

Thanks

[keyur trivedi]

Well no this is not the same machine but similar one. In last one i used two seperate cylinders and dcvs for dirlling and boring, because head was travelling in that and job was stationary. Here i have used one cylinder and dcv. Extention stroke of cylinder is for drilling. and retention is for boring. In this machine job is moving. Well Both the directional valves are YUKEN(japan) made, and model no. for both is DCG-01-3C60. While both the flow control valves are REXROTH(germany) made and model no. for both is 2FRM6V36-20/10QRV. The problem you said last time can occure with any valve. Back pressure can't be reduced since it's a meter out circuit. So what steps should i take to cure the problem? Should i change anything in my design? will counter balance valve work in this? since it creates extra drop befor oil enters the valve against the back pressure drop created by flow control valve. In rapid motion only or when the dcv for feed valve(valve 3) is not on, there is no any problem. But as that valve starts the problem starts. So please guide me through this. Thanks!

Regards,

keyur trivedi

[Doug Hanson]

I think your problem is the spool. Double check with Yuken, but with Hystar the 3C6 has all ports blocked in transition, the 3C60 has all ports open during transition.

[Doug Hanson]

Attached is how I would draw this system up if all of the valves were to be located on one common series manifold. The transitions positions of the valves are not shown, but I would use the 3C6 spool as opposed to the 3C60, and as discussed in previous posts, I would use a sequence valve and accumulator for the clamping circuit, which is not shown.
If you expalin to your valve supplier that you just need to do a conversion on your valves, they may sell you just the spools although some companies do not like to do this.

[keyur trivedi]

Thank you mr. doug. I think this is the problem i faced in every power unit. Today i got sollution. I am going to change the valve soon, let's see what happens. And i have one question in my mind if 3C60 creates surges then what's the reason they are in market?

Regards,

keyur trivedi

[Doug Hanson]