Riviera leaking past piston seals

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
User avatar
cuppajoe

#1: Post by cuppajoe »

Still beating my head against the two group Riviera. Got most of it sorted, but still have persistent leaking once it starts to come up to pressure. What is odd is that the leaking usually stops once it's up to pressure.

So far I've disassembled both groups about eight times. The piston seals have been replaced with the larger version. The bores have been honed and polished. The piston and rod assembly was replaced in one group. The last thing I tried was wrapping the seal indents with teflon tape, so I've pretty much run through the options.

I'm having a hard time wrapping my head around the engineering, if all parts are original. There are three piston seals, the top one facing down, the middle facing up, and the bottom facing down. The water inlet to the group lands just below the top of the middle seal when at rest. This allows boiler pressure to force water past the seal and on to the bottom seal, which also faces down. Looking at the piston it seems a more effective design would be to have the inlet above the middle seal, trapping the water between the middle and top seal. That would prevent water from leaking past the bottom seal when at rest.

Any input towards a solution would be greatly appreciated.
David - LMWDP 448

My coffee wasn't strong enough to defend itself - Tom Waits

RobAnybody

#2: Post by RobAnybody »

Still the same riviera as the one which had the the hacked up piston?

My guess would be that while the machine pressurizes the piston rod also warms up and extends a bit so at the end the water inlet sits just above the top of the middle seal..
Do you still have a bit of space between the piston and the showerscreen or is it flat against the screen in the down position?
Is there a bit of extra room in the groove of the middle seal? if so you could place a backing ring above the middle seal which pushes it down a bit so it ends up just below the water inlet.
cheers!
Rob
LMWDP #647

User avatar
cuppajoe (original poster)

#3: Post by cuppajoe (original poster) »

Hi Rob -

First off, thanks for the reply.

Yes, same machine. I've been having to wait on the owner to ensure he's on board to complete the repair. This machine has been tampered with, so unsure as to how original it is. At rest the piston sits just shy of the shower screen. Your idea of trying to space the middle seal further down is worth exploring. I may research seals to try and find a replacement that is a bit thinner, maybe even an O-ring. Having the water inlet a mm or so higher than where it is would have eliminated the problem.

Cheers

David
David - LMWDP 448

My coffee wasn't strong enough to defend itself - Tom Waits

RobAnybody

#4: Post by RobAnybody »

with a bit of luck (and maybe some swearing) you could fit something like this above the middle seal
https://www.globaloring.com/product/sp213/
it should provide you the extra mm. Hopefully the expansion of the seal due to the compression won't increase the resistance to much (the flexibility of the lip should takecare of that).
With an O-ring you'll probably have to make a kind of filler construction to mount it on the piston (since the OD is 40mm, height 6.5mm and the diameter of the piston groove is 24mm)
cheers,
Rob
LMWDP #647

User avatar
peacecup

#5: Post by peacecup »

We had a similar discussion about the Sama Export recently. The original design is robust, with the inlet port resting between two opposing seals when the piston is at rest, as seen in the picture:



If changes have been made that in some result in the piston being just a little off-location when at rest, the port may not function as intended. Maybe you can flip the lever yoke to allow the piston to rest a little higher or lower. Even a roller bearing of a different thickness will affect where the piston rests.
LMWDP #049
Hand-ground, hand-pulled: "hands down.."

User avatar
cuppajoe (original poster)

#6: Post by cuppajoe (original poster) »

Rob - That looks like a good candidate, unfortunately they are out of stock. I'll poke around and see if I can find an equivalent.

Peacecup - The illustration was what I would have expected. The pivot hole in the yoke was close to center, but I tried flopping it anyway. It ended up moving the piston too close to the screen. Moving the piston down is the only way to overcome the spacing of the inlet port, so a bit of a catch 22. Trying to move the middle seal seems to be the only option. If I had access to a lathe I'd try widening the middle seal land so the seal could be moved further down and make it easier to add a spacer.

Thanks again for the tips.
David - LMWDP 448

My coffee wasn't strong enough to defend itself - Tom Waits

User avatar
peacecup

#7: Post by peacecup »

What about boring a new hole in the piston rod to adjust the height?
LMWDP #049
Hand-ground, hand-pulled: "hands down.."

User avatar
cuppajoe (original poster)

#8: Post by cuppajoe (original poster) »

The problem is in order to bring the lip of the seal below the inlet port the piston needs to be lowered, which brings the bottom of the piston below the shower screen location. As it is now, the piston is at the correct height in relation to the cylinder bore, but not the inlet port. It's like the group and piston assembly are from two different machines.
David - LMWDP 448

My coffee wasn't strong enough to defend itself - Tom Waits

User avatar
cuppajoe (original poster)

#9: Post by cuppajoe (original poster) »

I just checked and there's not enough room to fit in a spacer. My next move is to try and source a seal with the same diameters, but just a tad thinner. Failing that, shave off a bit from the back side of the seal.

Failing that, pack the thing with C-4...
David - LMWDP 448

My coffee wasn't strong enough to defend itself - Tom Waits

RobAnybody

#10: Post by RobAnybody »

cuppajoe wrote:Failing that, pack the thing with C-4...
before that, sanding down the bottom of the piston.
That would be the only other option i could think of to be able to lower the piston a bit more.
LMWDP #647