Thread: Repair of hydraulic piston/cylinder

That plastic “wiper” could be a backup ring. Is the crack actually a crack or is it possibly a scarfed join to allow you to fit it into the groove.

Steve

Originally Posted by OxxAndBert

That plastic “wiper” could be a backup ring. Is the crack actually a crack or is it possibly a scarfed join to allow you to fit it into the groove.

Thanks Steve and China.

Have added pics to OP.
I had to mangle the ring and wiper to get them out so they look much more beat up than before removal.

Not sure about about the wiper crack - whatever it was it definitely had a break in the continuity.

Hard to tell from the photo, but the backup rings I've dealt with in the past (aviation) were Teflon. They were typically scarfed so they could be spread over a shaft and placed in the groove and the ends would overlap when in position. Some were thinner and did almost 2 turns so there was a continuous contact - looked a bit like a double turn spring washer.
The idea is they are used on the opposite side of the o-ring to where the main pressure is applied to prevent the o-ring extruding down between the shaft/piston and bore.

Steve

CBC got back to me this morning and said its a non-standard O-ring (12.7mm ID and 2.3mm) - could be a 1/2 x 3/32" but they will try and source one for me.
Good service.

Originally Posted by OxxAndBert

Hard to tell from the photo, but the backup rings I've dealt with in the past (aviation) were Teflon. They were typically scarfed so they could be spread over a shaft and placed in the groove and the ends would overlap when in position. Some were thinner and did almost 2 turns so there was a continuous contact - looked a bit like a double turn spring washer.
The idea is they are used on the opposite side of the o-ring to where the main pressure is applied to prevent the o-ring extruding down between the shaft/piston and bore.

Steve

Thanks Steve, I have some teflon rod so if push-comes to shove I can probably turn one up.

Got a quote from CBC,

Price of O-ring is $23.40, minimum order is 10 pieces, has to come from US Freight is $50 pls GTS $316

For $100 I can buy a whole brand new pump.

https://www.sjscycles.co.uk/pumps/to...mm-id/?geoc=AU

Originally Posted by SurfinNev

https://www.sjscycles.co.uk/pumps/to...mm-id/?geoc=AU

Thanks SN, about 10 minutes ago I found my missing box of O-rings and found two of that size.
I also found a short piece of teflon rod to have a crack at making the wiper.

Here's my attempt at turning the teflon wiper for the press pump.

Had bugger all length of teflon rod of the right diameter to play with.
Required dimensions of the wiper were 12.7 ID, 17.3 OD and 1.25 mm thick,

Here it is turned down to OD and bored out to ID using a milling flute.
Wiper3.JPG

Standard parting tools too thick so resorted to the old hacksaw blade trick.

Needed 1.25,m thick but was worried the teflon might move so cut it overside and it came out at 1.42mm but this hard teflon (PTFE) sands really vice so I was able to drill an 18mm diam x 1mm deep flat bottom hole hole in a piece of wood using a Forstner bit and inserted the wiper into the hole and rubbed it back and forth on some 180 grit paper.
I even left that tiny little lip on the ID to act as an extra wiper.
Wiper3a.JPG

It was a bit tricky getting it and the O-ring into the internal ring groove but the teflon had enough flex to get in there without breaking.

Wiper3c.JPG

Press works - no drips - all good.

Great stuff, amazing what we can do if we have to, I really enjoy this type of repair

A week later and can report not a single drop of hydro has been lost from the pump repair.
Now I have to tackle the slave/ram which oozes a few drops a week if I leave it below a certain position.

You will put CBC out of business at this rate (Ha Ha)