Cushion Cylinder design

[Tnels]

I'm trying to design a very simple hydraulic circuit. Currently the hydraulic cylinder has capped in/out flow, and only acts as a cushion for a tilt deck trailer. I need to stop flow while a load is driven/pulled onto the trailer. Is there any reason I can't just place a needle valve in between the in/out flow ports, with hoses, to stop flow? I've seen other systems that use a reservoir. Is the reservoir needed or am I missing something?

I understand that the current cylinder has a relief hole in the piston. For my purposes I am planning on using a cylinder without the relief hole.

 

[BEMPE16524]

The reservoir serves multiple purposes:

• Provides a buffer for thermal expansion and volume changes.
• Ensures there is always sufficient fluid available to compensate for small leaks.
• Helps maintain system pressure balance.

Without a reservoir, you are at risk of overpressure, fluid leakage, and eventual system failure due to temperature changes.

 

[LittleInch]

Try drawing up a simple diagram so that we can all understand what you mean, where the reservoir night be, where the pump nis and where you want to place your valves.

What's a cushion? Its purpose, load etc.

Is that like a hydraulic spring? Needs a diagram.

 

[Tnels]

The reservoir serves multiple purposes:

• Provides a buffer for thermal expansion and volume changes.
• Ensures there is always sufficient fluid available to compensate for small leaks.
• Helps maintain system pressure balance.

Without a reservoir, you are at risk of overpressure, fluid leakage, and eventual system failure due to temperature changes.

So even without using a pump you would still recommend a reservoir? Any recommendations on how to tie it in? Would I need a 3-way 3-position valve or something similar?

Try drawing up a simple diagram so that we can all understand what you mean, where the reservoir night be, where the pump nis and where you want to place your valves.

What's a cushion? Its purpose, load etc.

Is that like a hydraulic spring? Needs a diagram.

This is what I'm thinking I need (Not to scale). The cylinder does not push at all. It is only to cushion the fall of the trailer deck when a vehicle is driven onto it. The cylinder will rotate forward (Left in diagram) as it retracts.

 

[BEMPE16524]

I believe what you mean is not really the pump reservoir. it is more likely a compensator that will expand when oil is full and contract by means of spring to fill up the system.

I used something like this in one of my system:


but you must know the maximum weight of your load and the capacity of the bellow compensator before it explode.

 

[akkamaan]

As some others say, it is hard to understand your idea exactly. But here is my interpretation...
The way you have drawn the schematic the needle valve fills no function. I assume you have put the needle valve there to control flow from the capped side to the rod side. That won't work since oil displacement is bigger on the capped side than the rod side can receive. The volume of the rod is the difference. Enev the most leak-free piston seal will by time leak oil (read pressure) through the seal and the pressure will be determined by the mass resting on the cylinder and the piston rod's diameter (read cross-section area).
To use the cylinder as a dampener, you need to drain the capped side via the needle valve to a reservoir. It also needs to have the rod side vented to the reservoir.

Does the capped side refill when you unload from the deck?
If you need to dampen the tilt-up when unloading you will need a "needle valve" on the rod side as well.
I would use one-way check valves in combination with the needle valves. That way the cylinder can refill without flow restriction both ways