Is there a gas strut kind of thing that can be used outdoors, and is not effected by temperature?

[Emmette Kelly]

We have an application where we need to control the movement of an 800 pound piece of steel that rides on a track that can move 15 inches in a straight line, up and down. The structure that it's mounted to tips, and when it does, this 800 pound piece of steel will slam against the stops after moving over that 15 inches on the track. This is obviously an issue. We need to keep that 800 pound piece of steel stationary, until another force acts on it, and causes it to move.

Initially, we had the idea of putting it on gas struts, like the hatchback of a car. The steel would not move until a force limit was hit, and then it would move slowly. The problem is that the pressure where the strut starts to move changes depending on the position of the strut cylinder, and the temperature. They also don't much like outdoor environments. Our product could be used anywhere from frigid cold to summer heat. We thought about springs, but springs have huge differentials in force depending on how much the spring is extended or compressed. In our application, once say 800 pounds of pressure is exceeded, we want the steel to move in a dampened fashion so nothing slams. When the pressure disappears, the steel returns to its resting position.

Does anyone have any thoughts to technologies or solutions that I can give to our engineering guy to see if they might work in this application?

Thanks

​

 

[rb1957]

magnets ?

a hydraulic strut would be much less sensitive to temperature than a gas strut. All gas struts are sensitive to temperature (P/T = constant).
there may be "temperature compensated" gas struts (that would add or vent gas depending on the temperature) but that sounds like quite the control system.

another day in paradise, or is paradise one day closer ?

 

[Compositepro]

Use a hydraulic cylinder. Supply it with oil from an air over oil reservoir. Adjust the air pressure to whatever you like. Use a needle valve to control the speed of the cylinder. A single acting cylinder should be all you need. You can use two speed control valves to have different extend and retract speeds.

 

[Emmette Kelly]

Can you use a hydraulic cylinder to not move until a certain pressure is reached, and then start to move slowly as governed by a needle valve?

 

[3DDave]

Counterbalance weight - if you use s smaller counterweight use a gear/pulley system so the 800 pounds goes down 15 inches and the counterweight goes up 10 feet, or some similar to get the desired ratio.

As far as springs go - look at the way garage door springs work, particularly in the last 15 inches of travel. There are a large number of initial turns so that the last bit is nearly constant force; otherwise you'd see the doors either fly open or the homeowner needed to dead lift after the first foot of travel.

 

[moon161]

I think still use gas struts. They did the job with a 200lb or so tailgate in all service for the first 30 or so years of my cars life, now they just work right above 70F or so. If I replaced them, they would last until internal combustion cars could only be used in special parks or the body turned to brown powder.

They are temperature sensitive, but if your temp range is 20C +30/-60, your hot/cold service pressure ratio is 300K/210K or just shy of 1.5. Station wagons and minivans with giant tailgates have been working in this range for decades.

 

[MintJulep]

With such a vague description it is simply not possible for anyone to provide useful advice.

Hopefully your 'engineering guy' is actually an engineer.

 

[moon161]

I see that instead of like a tailgate, you're looking for a straight line vertical travel, should have read more carefully first time. You might fabricate a mechanism that gives you leverage over the unbalanced load, possibly with a toggle action to or other means to lock in place.

 

[rb1957]

I too missed the vertical nature, but also (as posted above) the problem is very loosely worded. As noted above, I think your "engineering guy" is going to be more use.

another day in paradise, or is paradise one day closer ?

 

[TheTick]

If you can take the T out of PV=nRT, you're good to go.

 

[BrianE22]

I've never used one but do a search on "temperature compensated flow control valve"

 

[Emmette Kelly]

But can a hydraulic cylinder not move until a certain pressure is reached, and then give way, the way a gas strut works? Or a shock absorber?

 

[Compositepro]

By adjusting the pressure in the air-over-oil reservoir that I mentioned above or a relief type valve.

 

[FacEngrPE]

If you need to absorb the slam energy, an elevator buffer or a buffer stop might work, but buffers by themselves can not index to an exact position.

Example

https://youtu.be/VkVlRk9Y4PU

 

[kjoiner]

Hello,

It sounds like you need a hydraulic damper not a gas spring. A gas spring has a damper effect but it is also storing energy when compressed. It sounds like you just need to dissipate energy.

I recommend contacting Ace Controls, H.A. Guden, Stabilus or Suspa. They have application engineers that can help select a damper.

Kyle