Can a 1 MPA valve handle the weight on a pneumatically adjustable massage table?

[Jason Doyle]

Hey guys,

First off, Id like to say that I am not an engineering student, I study Physical Therapy. I am wanting to make an old massage table I have pneumatically adjustable height wise. I was thinking of putting a 16 mm bore pneumatic cylinder inside each leg (Or possibly replacing the leg entirely with a 32 mm bore 300 stroke)

https://www.ebay.ca/itm/16mm-Bore-300mm-Stroke-Double-Action-Single-Rod-Pneumatic-Air-Cylinder/322047953457?hash=item4afb8dca31:g:Fe0AAOSwnCFaSyoL

Starting from a foot pump or bicycle pump, running hose into a 1 way or speed control valve 1 MPA (so the air pressure stays in the cylinder and the table height is maintained until valve is released) and then to a Y connector which would split to 2 more y Connectors and then run to each cylinder (Diagram Attached). Do you guys think this idea will work? I am curious if a 1 MPA valve will hold the weight of a person, as well as the M5 or hose Y connectors without bursting? Any advise you can give would be greatly appreciated!

 

[JBA]

Whether you can use a 1 Mpa valve depends upon the size of your selected 4 cylinders vs. the maximum load expected to be applied on the table. The formula to determine this is Max valve and system pressure = (Table Load x safety factor) / ((d^2 x π /4 ) x 4 cylinders)
where: d = bore diameter of the selected cylinder.

A couple of issues you will run into is to get all four cylinders to lift to the same height with one pump feed and even with a shutoff valve, the air cylinders are going to compress according to the amount of load and where that load is placed on the table. If you apply a load near one or two of the cylinders then those cylinders are going to compress and lighter loaded cylinders are going to extend by amount proportional to the differential load at each one.(i.e. you could end up with a bouncy table that also tilts when you apply pressure at different locations on the table.) One way to address these problems might be to install positive locks on all of the legs that can be unlocked for raising or lowering the table with your air lift system.

 

[anorlunda]

To get around the leveling problem @JBA mentioned, you might consider a scissor lift and a single pneumatic cylinder. Below is a picture of something similar.

 

[Jason Doyle]

Thanks guys, where did you find that picture Anorlunda, Perhaps Ill just purchase one like that instead (although it will be less fun)

 

[anorlunda]

Thanks guys, where did you find that picture Anorlunda, Perhaps Ill just purchase one like that instead (although it will be less fun)

images.google.com "scissors lift table"

 

[Jason Doyle]

Whether you can use a 1 Mpa valve depends upon the size of your selected 4 cylinders vs. the maximum load expected to be applied on the table. The formula to determine this is Max valve and system pressure = (Table Load x safety factor) / ((d^2 x π /4 ) x 4 cylinders)
where: d = bore diameter of the selected cylinder.

A couple of issues you will run into is to get all four cylinders to lift to the same height with one pump feed and even with a shutoff valve, the air cylinders are going to compress according to the amount of load and where that load is placed on the table. If you apply a load near one or two of the cylinders then those cylinders are going to compress and lighter loaded cylinders are going to extend by amount proportional to the differential load at each one.(i.e. you could end up with a bouncy table that also tilts when you apply pressure at different locations on the table.) One way to address these problems might be to install positive locks on all of the legs that can be unlocked for raising or lowering the table with your air lift system.

JBA, Since I don't know the safety factor force the aluminum alloy the legs are made of I did the math at 300 LB (this is at least 100 lb more then any of my patients) and cam out with .37 so if I understand a 1MPA valve should be more than twice the required pressure? Also on you last comment, the table is currently manually adjustable and has locks its just time consuming because each leg is done individually. I was thinking with the pneumatics, I would just ask the patient to jump up, pump it to the required height then resume. Thanks for your help so far on this!