Which piston reg is the best to practice rebuilding on? Preferably an SP reg.

[elan]

Halocline thanks for that information.

I have got the 2 DIN kits on ebay. They were a bit expensive (still less than the DiN kit I got for mk20 ) but I decided to bite the bullet as I needed DINs. they also have a metal thumbwheel.

 

[ams511]

I have rebuilt it today, reused the seat and the bushings, but replaced all 0-rings with new - I used polyurethane ones in for dynamic (except the second big o-ring on the piston) + DIN, and EPDM for the rest.

Are most people using polyurethane and EPDM O-rings for rebuilding first stages?

 

[Zung]

I do, because they're cheap and readily available, and I have a good stock fo them. But nowadays, Viton's are good too.

 

[ams511]

I do, because they're cheap and readily available, and I have a good stock fo them. But nowadays, Viton's are good too.

I remember from previous posts it was recommended to use 90 duro polyurethane on the 010 piston ring on the MK-5 and MK-10. Do you also use polyurethane on the large piston 022 and 017? Also do you recommend EPDM on the first stages?


Edit: Also didn't you guys get a bad batch of the polyurethane O-rings a while back?

 

[Slamfire]

Are most people using polyurethane and EPDM O-rings for rebuilding first stages?

I remember from previous posts it was recommended to use 90 duro polyurethane on the 010 piston ring on the MK-5 and MK-10. Do you also use polyurethane on the large piston 022 and 017? Also do you recommend EPDM on the first stages?


Edit: Also didn't you guys get a bad batch of the polyurethane O-rings a while back?

I use viton duro 90 on almost everything including the big and small piston orings. In addition to using -010 viton duro 90 in the small piston, I also use them on lp hose and as orifice orings for my G250s. They are a bit oversized for orifices, which can make it challenging to install, but they work well. I like viton for its long shelf life. It enables you to buy baggies of 100 orings and not worry too much about them getting too old on you. And they are cheaper than PU.

 

[Zung]

I use PU 90 on the piston shaft because it was the only game in town then. I don't use PU anywhere else because they're very expensive, and their shelf lifes don't seem to be too good; I use EPDM because of their availability and because that's what SP uses.

awap got a batch of PU's from O-rings USA and many of them were bad. I got some a couple of years ago from McMaster and they're still good, just looked.

Today, if I had to reorder, I'd go for the Viton because they're $9.65 for a 100, and the PU are $14.82 for 25. both prices from McMaster.

 

[halocline]

I use 90s wherever there's high pressure involved and 70 where there's not. I was in on that order of 90 duro polyurethane, several of mine were bad as well. But the good ones worked great. There was some discussion of viton's poor reputation for extrusion resistance, but then someone (maybe couv) pointed out some specs that indicated otherwise, so who knows what compound is really best for that HP piston o-ring. I have read somewhere that 70 duro might work a little better in LP situations because they're more flexible, but who knows on that one as well.

For high O2 concentrations, viton for sure but otherwise I suspect EPDM is perfectly fine. (SP has used them for years) They both have very long shelf lives.

 

[elan]

BTW: Speaking of the IP drop after the lockup I think what Zung said make sense, I was thinking about it and I think after the lock is secured the IP still pushes the piston further and because the piston has locked already the amount of air stays the same but the volume of the space increases with the piston move. So the IP drops a bit....

 

[halocline]

BTW: Speaking of the IP drop after the lockup I think what Zung said make sense, I was thinking about it and I think after the lock is secured the IP still pushes the piston further and because the piston has locked already the amount of air stays the same but the volume of the space increases with the piston move. So the IP drops a bit....

I don't think so....The volume increase, if any, is extremely small, probably not measurable without expensive lasers or something like that. The seat is hard plastic, not soft, the piston might move a fraction of a thousandth of an inch and the IP chamber is a fairly high volume area including the inside of all LP hoses.

Maybe the hoses expand a little, that could explain it I guess. The air has to go somewhere or significantly cool for there to be a pressure drop in the IP chamber.

 

[elan]

I don't think so....The volume increase, if any, is extremely small, probably not measurable without expensive lasers or something like that. The seat is hard plastic, not soft, the piston might move a fraction of a thousandth of an inch and the IP chamber is a fairly high volume area including the inside of all LP hoses.

Maybe the hoses expand a little, that could explain it I guess. The air has to go somewhere or significantly cool for there to be a pressure drop in the IP chamber.

I guess you are right, hoses expansion makes more sense.

Now I recall my Zeagles do the same they drop about 3-5 psi after 20-30 mins. My theory could not explain that as they are upstream valves and if my theory was correct the IP would have to rise