Looking for oil pump piston packing

[rke[pler]

I've got a Lagun FT-2 mill with an integral one-shot oil pump. The pump is slowly going bad. I have a replacement I found on eBay some time ago, problem is that the seal on the piston is gone. Looking for a replacement I found that the seal ID is .496"/12.6mm, seal OD is 20mm and width is .240/6.13 so I don't know if I should be looking for an inch or metric seal. The rod seal seems metric with a 8mm/14mm id/od and 4mm thickness so I expect the whole assemble should be metric, so should I be looking for a 12.5mm/20mmx6mm seal?

 

[atex57]

Did the seal measure 12.6 mm or did the piston it mounts to measure that? Always measure the metal parts. I have a book that shows a LOT of metric seals.

Ed.

 

[ratbldr427]

Check out Metric Seals inc in Indiana. Their online catalog shows just about any metric seal available. A little hard to navagate at first. Look carefully at the seal and if any no.'s are on the outside if not then look inside the lip. Just about all metric seals have pn's that are also the size; id x od x width (which may have several no's if it is stepped). You will often find many that interchange and many that the difference is the material or in the width (which is easy to accommodate by machining or adding a spacer).

Or just call them and give them the info.

 

[rke[pler]

Like I said, the pump came with the piston seal missing so no chance getting the original seal part number is not possible.

I'll try Metric Seals and see if I can find something suitable.

 

[Garwood]

Looks like an O-ring groove to me.

Try a 12mm ID 4MM section O-ring.

 

[Bill D]

Any idea on brand of pump. Laugn is Spainish so I guess metric unless it is a English pump.
Bill D

 

[rke[pler]

Looks like an O-ring groove to me.

Try a 12mm ID 4MM section O-ring.

I thought of that but figured the ring interference on the inside would give too much compression on the 20mm bore.

 

[Garwood]

I thought of that but figured the ring interference on the inside would give too much compression on the 20mm bore.

.3mm compression on a 4mm ring is way under compressed. That should slide easily.

For a 12 cent O-ring seams easy enough to try no?

 

[ratbldr427]

O'rings are quite forgiving in that type service, so grab a few and try them. I have had to do that many times when all else fails with good results.

There are some types of simple pumps where a cup seal serves as an inlet check but yours appears to have an inlet an outlet check.

 

[true temper]

Or make a new piston to fit an easily sourced Oring.

 

[r1xlx]

The pump is for a milling machine not the Space Station so absolute precision of fit isn't important.
Orings are actually sized as bore x cross section and all can be stretched.
You pump needs a ring with good stretch and the best is probably a 16 bore x 2.5 cross section which will give an o/d of 21 and fit snug in the groove.
I had to learn orings pretty quick when i started at a big valve shop and had to machine an oring groove in face of a thick steel disk. Never done it before so I asked foreman how deep and wide the groove should be and was amazed when he said something like 140 thou deep and wide for a ring cross section that measured about 160!
I couldn't believe that a round oring of 160 section could fill the 140 square groove and still seal but sure enough the test guy turned the pressure real high and it sealed.
Presumably a oring is pushed by the pressure of the liquid or gas the way a piston ring is?
Sometime if a valve needed a nonstandard oring we made one by supergluing nitrile cord with a diagonal splice joining.

Anyway Ebay has masses of suppliers of orings.

 

[rke[pler]

I've used O-ring and X-rings on pistons in live steam on brake cylinders and axle-driven and steam-driven water pumps and even when pumping against 125 pounds of pressure used only .006" diameter compression on the rings, so I figured .6mm on diameter (.024") might be a little much. Maybe the oil will make a difference.

Backers on each side of the ring? The bottom corners of the groove are squarish and I might want to limit ring roll a bit.

I'll swing by a local hydraulic shop and see what we can put together.