Sequence Valve Chattering

[ayoung802]

I've recently completed a large hydraulically actuated door on a yacht. I used a sequence valve to make it a two step process. The first step unlocks the dogging cylinders followed by the opening of the transom door. We have built similar doors in the past, but on a smaller scale with success.

We've run into an odd problem this time around. When the door is on the upswing about half way up it starts to vibrate and chatter, but then smoothes out again. We spent a bit of time scratching our heads over this one and still have no solution.

-When we isolate the dog cylinder circuit the door opens smoothly. So I believe we can eliminate the possibility of a problem with the opening cylinders, or a problem with geometry.

-Next, because of the previous discovery it lead us to believe something was wrong with the dog cylinders. We tested each one to make sure we didn't have a bad cylinder that was leaking fluid, but none of the cylinders were passing fluid.

-This lead us to believe there was a problem with the sequence valve. We changed the cartridges out and still experience the same problem.

-We did remove the check valve from the direction control stack because we added a counterbalance valve to each cylinder. The counterbalance valves are there should the system fail the door won’t come crashing down. This did not change the systems performance.

Any ideas or help would be greatly appreciated. I've attached a schematic of the system.

We are using the following valves:
Parker Directional control valve D3W4CNJ
Parker Flow control FM3DD-KN
Sun Sequence valve RSDC-LAN-E8J

Thanks in advance

 

[gerhardl]

I am not a hydraulic expert, and not able to follow your schematic, but logically:

A chattering indicates clearly an uneven distribution of forces.

Case 1. This must either be an internal (oil hydraulic) unbalance. Could be that one or some of the valves by certain pressure differences has a transisiton position 'undefined' (pilot operated valves pressure requirements?), or return pipes or ports are to small, or return in the system is influenced by return oilpipes combined, given too high back pressure at certain points/conditions.

Case 2. Could also be that forces (gravity weight, counterbalancing the hydraulic) after all is influencing, or the force at a certain point is too low. (Unforeseen underdimension of cylinders, pipelines, ports or valves at some point)

Since the operation runs smoothly under certain circumstances and/or for part of the operation it is unlikely that blockage within the system by dirt or similar contributes to the problem.

What happens if you increase the system pressure?

 

[ayoung802]

Gerhardl,

Everything in the system is rated to 3000 psi except the smaller dog cylinders which are only rated to 2000 psi. The dog cylinders have no acting load and only require a small force to retract. The door opens just about at 1000 psi. We have tried adjusting the flow control settings and the sequence valve settings, but it is either too low for the system to open or we get chattering. I will look over the system for any back pressure build up, but I believe I sufficiently sized everything. It also seems to me if back pressure were the problem we would see chattering even if the dog cylinder circuit is isolated. Now it could be the transition position of the sequence valve, but we played around with the sequence valve setting and replaced the cartridges. If that was the problem I believe chattering should still be present when the dog cylinders are isolated. Can anyone comment one way or the other?

I don't believe the cylinders are undersized, they can create 9000 lb lifting force each and the door only weights 3000 lbs. Plus there is a lot of mechanical leverage in the system. Due to the system layout, the cylinder force requirement does decrease as it opens, but increases again before it is fully opened. If that where the problem it should be present whether or not the dog cylinders are isolated.

Thanks for the ideas Gerhardl I’m looking into a couple different things.

 

[ayoung802]

Actually I take that back the required force to open the door is always increaseing until it is fully opened.

 

[Compositepro]

I sounds like there is too much elasticity in your hydraulic system with the dog cylinders in the loop. This could be air in the lines or cylinders or too much elasticity in the hoses.

 

[ayoung802]

Compositepro,

You might be on to something there. I was thinking what about the compresibility of the fluid because we have long runs to the dog cylinders, but I couldn't ever convince myself one way or the other, but I didn't think about flexibility of the hose.

The long runs are suppose to be S.S. tube, but I didn't get to see them install the runs before they were covered up. So if hoses were used instead of tube do you believe we would see that chattering in the door? What would be a possible solution? Change out the hoses for tubes?

Thanks

 

[MikeHalloran]

It might be sufficient to just bleed the air out of the dog cylinders. You did specify bleed ports, right?



Mike Halloran
Pembroke Pines, FL, USA

 

[gerhardl]

...ayoung802. Please inform when you solve the case!

I am also leaning towards the most possible explanation as given by compositepro, with possible air again as the most likely! (Should have thought about this simple explanation myself!)

 

[ayoung802]

Will do, but the Yacht is already gone and it might take a bit of time for us to catch up with it and make changes. I'm trying to get possible solutions now.

 

[ayoung802]

So to follow up we never found the problem. We bleed the system over and over to make sure all the air was out of the system and we didn't see a change. We replaced the sequence valve cartridges and the counter balance cartridges, no change.

The final solution we came up with is just separate the two systems. So we added another valve stack and an additional electrical button to operate the sequences. One to open and close the dogs one to open and close the garage.

I wish we could have gotten to the bottom of the problem, but we build one of a kind so there is no time to test and prototype. If I had to guess the problem was due to flexibility in the hose lines. I specked out tubing runs with small one foot hoses to each dog cylinder, but instead hoses between 5 and 10 ft were run to each dog.

 

[gerhardl]

Thank you for reporting back! Seems logical to me, there must be some residuent flexibillity in such (unusual?) long hoses, and a reason firm tubing is normally used.