Does anyone have experience of calculating piston ring leakage where the piston movement is linear as well as axial so the contact line between piston ring and cylinder is constantly changing. My problem is that the piston leakage is in a hydraulic system with a flooded cylinder and operating pressures of up to 400bar. All journals I find are on IC engines and so the theory is very different.

There are also differences in piston config, the piston I am looking at has one ring whereas a IC engine piston has numerous piston rings designed to do different things.

So, anyone know how to work out the pressure distribution against the cylinder wall and also if it is possible to relate fluid mechanics at such high pressure where leakage is at fairly high velocity, basically the fluid is getting blasted through the split line in the ring and the ring isn't expanding to the bore of the cylinder during the angular movement of the piston.

Cheers
Gordon

Dear Mr. g123
A scientific reply can serve as a "Partial Fulfilment for a PHD degree"
it is leakage between Sliding Concentric and Eccentric Plates, type of Rings (Cast Iron ar others,Speed dimensions length),Pressure variation,
Viscosity and more.
I can not help you at this stage and forum.

Hi,the calculations you are looking for are in the newer Parker Heavy duty cylinder catalogs. This is a little late but hope it helps. The calculations are in the technical section of the catalog. (cast iron ring leakage)etc.

Brettl3, can you post a link to it, all I have found so far is:

Cast Iron Piston Rings
Cast iron rings are the standard piston seals for Series 2H cylinders.
They offer the widest operating conditions by tolerating high operating
pressures, wide temperature range and are compatible with most
fluids. The only drawback of cast iron rings is that they allow a small
amount of leakage. The leakage for a 4" bore cylinder, operating at
2000 psi, with mineral base hydraulic fluid will be less than 10in3/min.
Leakage will increase as pressure, bore size and viscosity of the operating
hydraulic fluid increases. For these reasons cast iron rings are
not recommended when using water or (H.W.C.F.) fluids.

I would not only like to know the leakage as a function of pressure but the friction.

Hi Doug, I will try to find the catalog I spoke about. I remember it was a recent (maybe 5 years or less) printed Parker heavy duty cylinder. I researched the info for a couple of hydraulic applications we currently have here at the paper mill. Brett

quote:

Originally posted by Doug Hanson:
Brettl3, can you post a link to it, all I have found so far is:

Cast Iron Piston Rings
Cast iron rings are the standard piston seals for Series 2H cylinders.
They offer the widest operating conditions by tolerating high operating
pressures, wide temperature range and are compatible with most
fluids. The only drawback of cast iron rings is that they allow a small
amount of leakage. The leakage for a 4" bore cylinder, operating at
2000 psi, with mineral base hydraulic fluid will be less than 10in3/min.
Leakage will increase as pressure, bore size and viscosity of the operating
hydraulic fluid increases. For these reasons cast iron rings are
not recommended when using water or (H.W.C.F.) fluids.

Doug, I found the PDF file page to go to (Sec.2:21),page 21 of 54-hope this helps, Brett (http://www.parker.com/literature/Industrial%20Cylinder/cylinder/cat/english/HY08-1114_C_F.pdf

Hi, the graph with leakage and friction is on the following Parker PDF.http://www.parker.com/literature/Industrial%20Cylinder/cylinder/cat/english/HY08-1114_C_F.pdfHope this helps,Brett

quote:

Originally posted by Peter Nachtwey:
I would not only like to know the leakage as a function of pressure but the friction.

Thanks brettl3. I found that on the Parker site earlier, but there doesn't seem to be any accurate information on leakage calculation.

quote:

Originally posted by brettl3:
Hi, the graph with leakage and friction is on the following Parker PDF.http://www.parker.com/literature/Industrial%20Cylinder/cylinder/cat/english/HY08-1114_C_F.pdfHope this helps,Brett

quote:

Originally posted by Peter Nachtwey:
I would not only like to know the leakage as a function of pressure but the friction.

Found this in the telescopic catalog:
Pass/Fail criteria if not noted on Assembly drawing is as follows:
Cast Iron Rings Normal Maximum leakage 1 GPM.
Bypass = 1/2 cubic inch per inch of bore diameter per minute.
Extend bypass would be 1/2 cubic inch per inch of plunger piston ring OD
per minute.
Retract bypass would be 1/2 cubic inch per inch of piston ring OD per minute
of each stage added together.
Example SD73 Series;
Extend bypass; 1/2 x 5.25 = 2.62 cubic in / min.
Retract bypass; (1/2 x 7.25) + (1/2 x 6.25) + (1/2 x 5.25) = 9.38 cubic in / min.

No friction info yet.