replacing mk200 hp seat

[runsongas]

took apart a mk200 for practicing reg servicing. the reg was a little leaky before i started. cleaned it after disassembly and everything seemed dandy. I replaced the o rings and checked the hp seat (was a little bit grooved). I put it back together and it is leaking pretty badly from the vent holes on the LP side. I figure I need to replace the hp seat. how do i remove the old seat cleanly? and are there any diy options for a replacement seat? thanks

 

[redacted]

took apart a mk200 for practicing reg servicing. the reg was a little leaky before i started. cleaned it after disassembly and everything seemed dandy. I replaced the o rings and checked the hp seat (was a little bit grooved). I put it back together and it is leaking pretty badly from the vent holes on the LP side. I figure I need to replace the hp seat. how do i remove the old seat cleanly? and are there any diy options for a replacement seat? thanks

I would suspect it an o-ring (or sealing surface) problem. An HP seat problem would vent through an OPV rather than ambient holes.

No DIY HP seats that I know of but that seat is common to many unbalanced piston 1sts and Trident produces an aftermarket version that works. A few online dealers sell them.

 

[runsongas]

I figured it had to be the hp seat since I replaced all of the other o-rings. any advice on how to figure out where the leak is coming from? I copied the oring sizes from the mk2 guide that wolfpackdiver posted. Everything seemed to fit well, but did I screw up the sizing?

 

[redacted]

I figured it had to be the hp seat since I replaced all of the other o-rings. any advice on how to figure out where the leak is coming from? I copied the oring sizes from the mk2 guide that wolfpackdiver posted. Everything seemed to fit well, but did I screw up the sizing?

Always good to compare the size of old and new o-rings. While you may be able to get away with a + or - size in some cases, it looks like you did not. The Mk200 has a larger piston head than the Mk2. It takes an 023 according to my notes. If you do a search on Scubapro o-ring sizes, you will find a thread on the subject.

BTW, the HP seat is pushed out with a dulled straight pich through the piston head.

 

[runsongas]

thanks for the help, i didn't realize the mk200 had a different piston size. a lot of my googling had people saying the mk200 was just a mk2 with less ports.

---------- Post added May 15th, 2014 at 10:58 AM ----------

023 would be the bottom oring for the piston right? i think i put a 022 in that. will try to find a 023 and see if it helps

 

[halocline]

It would be good to get an IP gauge and a drawing so you can see exactly how the air flow goes in this design. If air is leaking out of the ambient chamber holes, the only place it can be coming from is either of the piston o-rings. But the seat could be leaking as well, and the IP gauge will tell you that. If the IP creeps up rapidly when you pressurize, the seat is leaking.

These are pretty simple regulators, not much to figure out. I think the MK200 is a smaller piston than the MK2, but I'm not 100% sure on that.

 

[axxel57]

It would be good to get an IP gauge and a drawing so you can see exactly how the air flow goes in this design. If air is leaking out of the ambient chamber holes, the only place it can be coming from is either of the piston o-rings. But the seat could be leaking as well, and the IP gauge will tell you that. If the IP creeps up rapidly when you pressurize, the seat is leaking.

These are pretty simple regulators, not much to figure out. I think the MK200 is a smaller piston than the MK2, but I'm not 100% sure on that.

Awap is right, it's a 023 o-ring for the bigger piston of the MK200.

 

[ams511]

i didn't realize the mk200 had a different piston size. a lot of my googling had people saying the mk200 was just a mk2 with less ports.

From the Scubapro website (timeline):

The MK200 is a slightly different version of the MK2. It has a piston head that is slightly larger than the MK2. The MK 200 has three low pressure ports, one high pressure port, a large yoke and black knob with a MK200 sticker. There were two versions: the first version, 1988-1991, has an S.P.E.C. cap and an optional rubber S.P.E.C. boot was offered for this regulator and would also fit the end cap of a MK2 first stage.

---------- Post added May 16th, 2014 at 05:22 PM ----------

I figure I need to replace the hp seat. how do i remove the old seat cleanly? and are there any diy options for a replacement seat? thanks

Scubatools makes a specific tool for the purpose but I use compressed air to force it out. Make sure you put a bag over the seat to catch it when it shoots out. As far as DIY options for the seat. You can flip the seat and use the other side if it was not used previously. Also Trident makes a replacement that is sold by VDH or NESS.

---------- Post added May 16th, 2014 at 05:24 PM ----------

I think the MK200 is a smaller piston than the MK2, but I'm not 100% sure on that.

The MK-3 used the smaller piston.

 

[bada3003]

FWIW, I used a MK15 for reg service practicing purposes and had symptoms similar to yours. awap diagnosed it correctly as piston o-ring leaking. In my case, the o-ring was the right size, just worn. Replacing it did the trick. The HP seat did cause an IP creep (you need an IP gauge to detect that), but replacing it with a new one solved the problem. I just pried it out (gently) with a brass pick. It's not gonna be reused to so scratching it further isn't an issue. However, be careful not to scratch the other parts of the reg.

thanks for the help, i didn't realize the mk200 had a different piston size. a lot of my googling had people saying the mk200 was just a mk2 with less ports.

---------- Post added May 15th, 2014 at 10:58 AM ----------

023 would be the bottom oring for the piston right? i think i put a 022 in that. will try to find a 023 and see if it helps

 

[ams511]

I just pried it out (gently) with a brass pick. It's not gonna be reused to so scratching it further isn't an issue. However, be careful not to scratch the other parts of the reg.

The seat on an unbalanced piston (MK2, MK200, MK3, AL Aquarius, etc.) is on the piston itself not on a carrier as on a balanced piston (MK5, 10, 15, 20, 21, 25). So the removal is different. You can also flip the seat on an unbalanced regulator.