piston sealing with port slotted cylinder

[picclock]

I'm in the process of designing a pump which needs to have slots cut into the cylinder for the inlet - similar in some ways to a 2 stroke.

Normally on projects like this I would just use a floating O'ring seal as thse seem to work well and live long. However a side port will likely rip it to pieces so I am left with few options.

1 to run the piston with no rings and hope that the good : fit will minimise the leakage.

2 to use cast iron piston rings, which I have no experience of, and I'm not sure I want to get into. It sounds like a very skilled manufacturing procedure.

3 random idea I came up with, to machine a groove in the cylinder wall and use an oring cylinder wall seal after the slots that the piston would seal with.

4 to ask the experts on HMEM :bow: who by rights should be fed up with my random pestering questions.

So I opted for 4 - many thanks HMEM members.

Best Regards

picclock

 

[vcutajar]

Hi picclock

I think I read somewhere that you can buy ready made piston rings for model engines. Maybe that could be your fifth option.

Vince

 

[cfellows]

You can probably get by without piston rings since compression on a pump isn't as critical as an engine. Obviously, the better the fit the more efficient your pump will be. Also kind of depends on how much pressure it has to work against. The higher the pressure, the better the fit needs to be. Otherwise, after a certain point, all the air will just leak past the piston.

What kind of application is this for?

Thx...
Chuck

 

[picclock]

The pump is a scavenger pump to recycle fluid/vapour mixture. Amazingly, to my small mind, I checked on ebay and there are loads of rings and even piston sets for this size, 40mm.

There is a chainsaw set with piston, wrist pin and ring for £12 delivered.

http://www.ebay.co.uk/itm/40MM-Pist...024?pt=LH_DefaultDomain_0&hash=item41644cada0

and many others for scooters, blowers and the like.

Which sounds nice and easy to me. The tubing I am using is just cold drawn 40mm, but will be more than good enough for this application. It appears that the 40mm size is used in many small engines so I think I have been very lucky, in fact spoiled for choice as this size seems to be used everywhere.

Many thanks for your interest.

Best Regards

picclock