Hydraulic piston repair

thehamo

Hey folks.

Not sure where I would have posted this so though id give DIY a shot! I have a hydraulic treatment table at home. One of the pistons of the table has stopped working and one section of the table wont stay up, keeps on falling down. Can anyone reccomend where I might get it fixed?

Cheers

_Brian

Are you sure it's the piston/ram.

I'd wonder if it's not the controlling valve not sealing properly an letting oil leak back.

Is the ram leakin oil out or just not holding.

thehamo

Im not sure il be honest. All I know is that it just wont hold at all. Doesnt seem to be leaking oil as far as I can see. When I extend it, it slowly just falls back into its self.

_Brian

Is the design so that the hydraulic force moves it up and then when you want it down it falls under it's own weight ?
Is there a pipe into one side of the ram only ?
That would make it a single acting ram - force in one direction only.

It sounds to me like the ram may be ok but the system isn't holding oil pressure to keep it in place and so it slips down.

whizbang

I suspect its one of these...? Not repairable.!

Having said that, the pins to release the pressure often get bent, or even jam in the mechanism, in which case, just pull out the pin and clean or straighten as necessary.

Also check the piston hasn't worked itself down its screw thread, so the release mechanism is pressed permanently against the release pin.

thehamo

whizbang wrote: »

I suspect its one of these...? Not repairable.!

Having said that, the pins to release the pressure often get bent, or even jam in the mechanism, in which case, just pull out the pin and clean or straighten as necessary.

Also check the piston hasn't worked itself down its screw thread, so the release mechanism is pressed permanently against the release pin.

Yep pretty much exactly that!

If unrepairable, how about replaceable? I had a look this morning and there seems to be a part missing I would imagine its pin to release the pressure

cerastes

thehamo wrote: »

Hey folks.

Not sure where I would have posted this so though id give DIY a shot! I have a hydraulic treatment table at home. One of the pistons of the table has stopped working and one section of the table wont stay up, keeps on falling down. Can anyone reccomend where I might get it fixed?

Cheers

I was going to suggest pictures, I thought this was some kind of hydraulic test rig and you were doing some other hydraulic work with it. I now read this as, its some kind of plinth or bed for people/other animals?

Still any pics? I suspect the hydraulic ram/cylinder is shorter and fatter than that shown?
Any leaks? is the ram straight? maybe its the pump? foot pedal? potentially some kind of seal or O-ring? maybe a cheap repair or direct to the manufacturer/ebay/look up sourcing the same diameter and length cylinder anywhere else?
Any part numbers on it (for your benefit for the searching above), manufacturers name?

is there only one cylinder? any others and does it/do they work? if so is there some control valve to direct one or the other to work?

thehamo

Thanks. As u can see in the pics its a 3 section table. The last section falls down and won't stay up. Its a hand release leaver to move the section up or down and should stay in place when the handle is released. What I can see is a pin on one side that gets pushed in when the hand lever is pressed but that pin is missing on the other side completely. Other than that I can see no visible leaks or anything of the sort. I'm looking about the internet for spare parts but its proving quite difficult

cerastes

the last section? Ive no idea which section you refer to as the last section, the head or the foot? I assume you mean the foot section (confirmed, I can see its the foot)

Do you think a part has fallen out? was it subjected to, a move? and so possibly damaged, excessive weight or force? did you see/hear or notice anything that may have indicated damage or did it just stop working?
Does anyone else clean up around it? and so may have thrwon out any part that might have fallen off? has any part been found?

I think a closer picture of the pin locations might help, it (the pin) may not need or may not meant to be on both sides.
Its hard to say without seeing it in front of me, but it sounds like the hydraulic cylinder does work, but a pin to stop it releasing pressure may be missing
It might be possible to get this part or even do some kind of repair, if thats acceptable for what you do, if its a business and you deal with customers itmight be that a new part is needed from a manaufacturer and the better option.

Maybe take some wide and closer pics of the hand lever and release mechanism and the pin/s you are talking about and how that interacts with the hydraulic cylinder.

thehamo

Cheers for detailed replies folks. I'd be dealing with customers so ideally I'd be looking at a new part. I'll take a few pics when I get a chance

CJhaughey

Its not a hydraulic ram, thats a pneumatic strut.
Hydraulic would have a pump to raise it and a valve to lower it.
Try this site, you need to measure the stroke length and overall distance and then the pressure it needs to provide.
http://www.strutsdirect.co.uk/
If the strut is one of a pair you may be best to buy two as they can become imbalanced otherwise.

KK4SAM

CJhaughey wrote: »

Its not a hydraulic ram, thats a pneumatic strut.
Hydraulic would have a pump to raise it and a valve to lower it.
Try this site, you need to measure the stroke length and overall distance and then the pressure it needs to provide.
http://www.strutsdirect.co.uk/
If the strut is one of a pair you may be best to buy two as they can become imbalanced otherwise.

I'd say its a ram, pump the pedal to lift and raise the pedal to drop ?

whizbang

If you are going out repairing these for customers, you probably should know this:

http://www.arjohuntleigh.ie/products/akron-couches/

cletus

whizbang wrote: »

If you are going out repairing these for customers, you probably should know this:

http://www.arjohuntleigh.ie/products/akron-couches/

I get the impression he treats customers on the table, rather than he has customers with these tables

CJhaughey

KK4SAM wrote: »

I'd say its a ram, pump the pedal to lift and raise the pedal to drop ?

I didn't see the pics OP posted, The one that I could see was a Pneumatic strut.
OP you should just contact the manufacturer and get the part from them.
It may not be much if the ram is still OK.

thehamo

https://www.youtube.com/watch?v=FPOj6YhX2nI

from about 1:12 in this is what I mean about having to pull a leaver to move the section of the bed

CJhaughey

thehamo wrote: »

https://www.youtube.com/watch?v=FPOj6YhX2nI

from about 1:12 in this is what I mean about having to pull a leaver to move the section of the bed

Why not contact them and ask about spare parts?

cerastes

Im trying to estimate what exactly is going on with it.

The more I look at it, these do seem like a pneumatic item, even though I think the youtube clip says hydraulic? but just how they are easily and rapidly operated by very slight or even no pressure or under their own pressure.

If there are no other connections or parts attached to the cylinder other than the release lever, then they probably are gas sprung and controlled by the adjustment lever and some connection at the cyclinder.
Id say the control is done by a direct connection of the release lever to the gas spring strut, it may be a cam or even only a slight rotation which controls relieving or locking pressure, either the connection is broken (missing pin you think?) meaning the internal operation of the cylinder cant be controlled (this might be an easy fix but be careful its done right).
Or
the connection is fine and the gas strut has lost pressure.

If thats the case and the part wont support the bed weight even though the control mechanism is connected (compare both gas struts) then it might be the part needs to be replaced. Although a small amount of lubricating liquid would be in there, it wouldnt be the complete available cylinder bore volume and probably wouldnt even leak out.
As no liquid has been detected, then this is probably part of the reason gas springs are used, rather than hydraulic,
Aside from their compressibility to not forcefully move someones weight or joints as they may have some give.

slimjimmc

The bottom cylinder (foot operated) definitely looks like it is hydraulic. The table moves in a very positive manner when the pedal is pumped whereas a gas cylinder would be springy and the table would sag when someone sits on it (like an office chair). The hydraulic fluid and pump piston are contained within the unit just like in an hydraulic car jack. It doesn't take much oil because the system makes use of the lever effect. If the table is sagging it could mean the piston seal is worn or a valve is leaking pressure back to the oil reservoir, either way you won't see an oil leak because it's all self-contained.
You could try a mechanic who repairs farm or construction machinery, he might be able to get spares if they're fairly standard dimensions.

cerastes

slimjimmc wrote: »

The bottom cylinder (foot operated) definitely looks like it is hydraulic. The table moves in a very positive manner when the pedal is pumped whereas a gas cylinder would be springy and the table would sag when someone sits on it (like an office chair). The hydraulic fluid and pump piston are contained within the unit just like in an hydraulic car jack. It doesn't take much oil because the system makes use of the lever effect. If the table is sagging it could mean the piston seal is worn or a valve is leaking pressure back to the oil reservoir, either way you won't see an oil leak because it's all self-contained.
You could try a mechanic who repairs farm or construction machinery, he might be able to get spares if they're fairly standard dimensions.

The raise lower of the entire bed height is hydraulic, Id say thats definite
but the raise lower of the upper and lower sections of the table/platform the head and feet sections, I think they are gas sprung struts.
Those struts arent operated by that centrally positioned pedal, but by their respective levers at each end.

slimjimmc

cerastes wrote: »

The raise lower of the entire bed height is hydraulic, Id say thats definite
but the raise lower of the upper and lower sections of the table/platform the head and feet sections, I think they are gas sprung struts.
Those struts arent operated by that centrally positioned pedal, but by their respective levers at each end.

I think they're lockable struts of the rigid locked type. The lever operates the rod going down the centre of the ram to allow fluid to pass through apertures in the piston and allow it to move. When the lever is released the apertures are closed and the piston is locked in place by the fluid on either side. If this isn't locking then perhaps the fluid is leaking past the piston or the lever mechanism is keeping it open.

http://www.stabilus.com/bloc-o-lift-with-rigid-locking-any-mounting/

cerastes

slimjimmc wrote: »

I think they're lockable struts of the rigid locked type. The lever operates the rod going down the centre of the ram to allow fluid to pass through apertures in the piston and allow it to move. When the lever is released the apertures are closed and the piston is locked in place by the fluid on either side.

They're used in this type of application.
http://www.stabilus.com/bloc-o-lift-with-rigid-locking-any-mounting/

Could be, I was thinking it would be a wholly compressed gas with a lockable arrangement, thats why I was suggesting the connecting mechanism may operate a cam or slightly rotate the cylinder or some part of it to allow pressure to act and to relieve it when movement is needed.

They should look at the cylinder and see what part numbers are there, start looking into a replacement part, but ID ensure the operating lever is connected correctly first.
If it is the strut/cylinder, Id suggest they consider getting a second one if both are the same as the other one could go be on the way out too. Although these things arent often cheap, it'd be there as a backup, at least noting the source to locate the part again and how long it takes in the event they detect the other strut is weakening or easier to move.

thehamo

slimjimmc wrote: »

I think they're lockable struts of the rigid locked type. The lever operates the rod going down the centre of the ram to allow fluid to pass through apertures in the piston and allow it to move. When the lever is released the apertures are closed and the piston is locked in place by the fluid on either side. If this isn't locking then perhaps the fluid is leaking past the piston or the lever mechanism is keeping it open.

http://www.stabilus.com/bloc-o-lift-with-rigid-locking-any-mounting/

This definitely looks like the thing im looking for. The pin down the middle seems to be missing from one of the struts. When the leaver is pulled, the pin is (or should be) pressed in allowing the section to be moved up or down, and when the leaver is released the pins are allowed to pop back up, if that makes any sense! Im going to be about later and il take more detailed pics and a video of what im talking about. But im pretty sure its the one above!

Actually from the above website...

"Application Example

Head and foot panel adjustments in hospital beds, operating tables, wheelchairs
Height adjustment in walker
Armrest, headrest, driver seat adjustment
Desktop/table height and inclination adjustment"

cerastes

Have a look and compare both those pin setups on both the top and bottom (head/foot) moveable parts, if they have the same (or even a similar setup) of cylinder and connection, you'll be able to compare to see if one item is missing something, if you could take a few pictures of the lever attachment point of at least the broken cylinder but preferably both cylinders and where you think the difference/missing pin is/should be.

Reason being, if the cylinder is just in its unlocked state due to some missing connecting pin, it may appear faulty/unable to resist any weight applied.
If the pin you are referring to is the entire center section the hand operated lever attaches to, to lock/unlock (which I would have thought less likely, but anything is possible) then you'd wonder how it went missing without being noticed, or even managed to come out if its connected/or covered/in contact somehow with the hand operated lever?

thehamo

Video and pics of the lever working the mechanism. As u can see hopefully as lever is compressed the pin is pushed into the strut and it can go up or down. Tho this is happening without even touching the leaver.

I got the site that sells the beds and they have spare parts. Only problem is it over in China so may have hastle getting them here

Sorry vid wouldn't upload

whizbang

Hamo, did you check the pins can be released? - the shaft of the piston has a screw thread ??

The gas springs have labels on them. maybe even have a part number already written on them?