Concerned about pressure spiking in scissor table

[negativ3]

Hi all,

First time post... hydraulics n00b.

I am looking to implement a table for handling machine tooling into and out of my home workshop. Basically off-loading from a pickup, transport 50 meters, then transfer to a bench. I am thinking a scissor table would be a way to do it, where loads are not suspended unnecessarily.

My concern is that when the table is raised to bed height, and the load is transferred from bed to table, the hydraulic piston will see a considerable spike in pressure, so what I want to do is:

1. Mitigate scissor downward movement under load transfer.
2. Limit chances of uncontrolled scissor collapse if hydraulics pop.

Any pointers would be fantastic with regard to correct valving/safety to incorporate, 3d representation attached of what I want to fabricate.

 

[3DDave]

I don't recall seeing any with the cylinder in that location. I suppose one could just use a screw shaft and a crank and eliminate the hydrualics altogether, but why the concern about the cylinder? If it's not overloaded it is just a mechanical element like the lift arms and their bearings.

Here's one non-hydraulic version

https://www.youtube.com/watch?v=szO3HPTzhU0

 

[negativ3]

A ball screw and a crank is a neat and kiss solution, thanks.

 

[hydtools]

As long as the pump release valve is closed the hydraulic fluid is blocked and the table will not drop with your load.
On that Enerpac pump you have to manually open a valve to allow oil to flow back and allow the load to drop.
Ted

 

[BrianPetersen]

Buy something that does this - don't build. All the stuff you are worried about has been dealt with already.

I have a motorcycle lift in my shop which is basically a scissor mechanism with a manual hydraulic pump, and a table on top of it.

 

[Jacc]

"My concern is that when the table is raised to bed height, and the load is transferred from bed to table, the hydraulic piston will see a considerable spike in pressure, so what I want to do is:

1. Mitigate scissor downward movement under load transfer.
2. Limit chances of uncontrolled scissor collapse if hydraulics pop."


1. Scissor will not move downward since oil is virtually incompressible, that is kind of the point with hydraulics. If it would have been a pneumatic cylinder it would be a problem.
2. Use a manual on-off valve in parallel with a check valve mounted directly to the cylinder to control the lowering of the load and to eliminate any risks with hose rupture. Use linkage to make the lever more accessible.

 

[akkamaan]

The spike on the piston will be lesser when table is raised to max height than the spike that will occur when table is almost at the bottom. Of course, the spike will only be induced when you drop the load onto the table. If you slide the load onto the table the won't be a pressure spike just regular load pressure.

 

[hydtools]

Reverse the cylinder mounting. Attach the head end to the rail where the pump is. Push to raise the table by extending the rod instead of retracting it as now shown. The hydraulic pressure will be lower for the same table load. The spikes, if any, will be lower because of the larger piston area compared to the rod end area.
Unless the cylinder gets in the way limiting the low height of the table.

Ted