MK10 IP Creep

[ocpaul]

I have a couple of MK10/G250 setups that I have used for about 12 years without too much problem. A year or so ago one of the MK10s started to put out excessive IP - I found the problem because my BPW wing kept overinflating. At first I thought there was a problem with the wing fill valve, but in the end found that the MK10 was putting out excessive IP.

The MK10 was serviced and all seemed to be OK. That is until a few weeks ago on a trip to Cocos Island. On a dive with a lot of surge I seemed to be having trouble maintaining neutral bouyancy - again my first thought went to the fill valve on the wing, but them my memory kicked in and I turned my suspicion to the MK10. Just disconnedted the hose for the remainder of the dive and then checked the IP after the dive (fortunately the boat captain had a suitable gauge) and found it to be about 165 psi. I understand that it should be more in the range of 140 - 145 psi???

Fortunately I had a backup on hand, so just swapped everything out and continued along my merry way.

Starting to wonder though, if this creeping IP is due to some damage to the MK10 that can't be fixed by replacing parts. I do remember on the first occurance that there was some kind of inlet screen, sort of looked like steel wool, that appeared to be corroded. Wondering if any of that material might have scratched a seat or something like that.

Finally - I was looking at posts relating to the MK10 and found a couple of references to SP instructions for this reg - went to the sites and could not specifically find the MK10. Is one of the other models essentially the same?

Thanks in advance for your insights! :14:

 

[Hallmac]

If you have the schematic Items # 22 and 36 (I think that is the numbers) is where I would look first. The piston #22 has two things that can happen. First salt build up on the shaft will nick the o-ring # 36, second a nick, scratch, or corrosion on the end will create a short HP seat life.

That is generally a solid unit. It may be time for a new piston and spring to extend the life.

Are you looking for a schematic?

 

[redacted]

This site has a Mk10 schematic: Deep South Divers! Come get wet with us! Select "Talk" and then follow the obvious path.

IP creep occurs when the knife edge of the piston has a hard time making a seal with the HP seat. Usually the problem is the seat has worn a groove and the piston has to travel further and cut deeper to lock up. Sometimes it may be a defect or crud in the knife edge of the piston. So first step is to get it serviced again. HP seats are readily available and if Scubapro is no longer supplying pistons, there are still some in stock at many shops.

IP creep normally develops over time (maybe years) and can easily be caught before it becomes a problem and interrupts a dive or dive trip. I check the IP on all my regs at least quarterly and before each dive trip.

 

[japan-diver]

A IP of 165 should not have been putting air into your wing though. Your octo or primary should start to free flow before the wing would be filling in most cases.

As others have pointed out the creep should be very fixable. It could be as simple as the tech nicked the oring when he installed the piston or as other mentioned you may need a new piston/spring.

 

[DA Aquamaster]

A nick in either the piston stem or piston head o-rings will cause leaks but will not cause IP creep as the leak would be into the ambient pressure chamber where it will then exit the reg.

In the Mk 10 IP creep is only caused by damage to the seat or the knife edge. The seat is a no brainer as it is replaced automatically at annual service. The knife edge on the end of the piston stem however may have a small nick in it that prevents the reg from locking up in the normal IP range. Some times you will get it to lock up at a higherthan normal range while other times it will continue to creep until the presure vents through one of the second stages. In some cases, the IP is normal shortly after the rebuild but the nicked knife edge may rotate slightly in service and them a leak occurs in the old part of the groove in te seat damaged by the nick.

The needle swing on an IP gauge will tell you a lot about exactly what is happening.

One of the best ways to detect damage on the knife edge is still to feel all the way around it with the end of your fingernail - you will be able to feel nicks that you can't see.

The damage occurs through dropping the piston or due to a chunk of the filter, salt, rust or carbon getting trapped between the seat and knife edge.

In the past it was not unknown to have to replace a Mk 10 spring due to the IP being out of spec and beyond what could be adjusted with shims (apparently they stiffen a bit with age) but SP now includes 3 different seats of different heights in their annual service kits to allow greater adjustment range.

Also, your inflator needs work as it should not be inflating due to an IP of only 165 psi.

 

[ocpaul]

Thanks for all of the replies and insights.

I did pick up the schematic and it certainly makes it understandable how everything works.

Thanks also for the comments on the inflator valve.

Follow up questions:
1. How much IP should a power inflator valve be able to stand off?
2. How much IP will normally cause a G250 to free flow?

OC

 

[halocline]

It's funny, I just pulled out my MK10 for a dive tomorrow and found the IP creeping steadily out of range after a few cycles on a full tank. I changed the seat (only had a used one) and the same thing happened. I then changed the piston (lucky me, I had a NOS piston sitting around) and problem solved, going back to the newer seat. The funny thing is that I recently bought the reg, rebuilt it and used it once without incident. Next step is to borrow a good strong magnifying glass and carefully check the knife edge on the piston I took out.

The reg came with a red, sort of translucent seal. I replaced it with one of the grey seals from a MK5 kit. I checked, and on my drawings the MK5 seat and MK10 seat are the same part number. What I hope is that I did not damage the piston in the MK10 by using a grey MK5 seat. I sure can't see any damage or feel any, but the magnifying glass will probably tell me for sure.

 

[DA Aquamaster]

Follow up questions:
1. How much IP should a power inflator valve be able to stand off?
2. How much IP will normally cause a G250 to free flow?

It depends how it is tuned.

If it is tuned so that it is just short of freeflow with the adjustment knob all the way out, it will freeflow with only about a 5 psi increase in IP.

If it is tuned with either the orifice or the inhalation adjustment to an inhalation effort of 1.2" of water (a slight turn on the orifice or 1 1/2 or 2 turns of the inhalation adjustment knob) it will freeflow after an increased of around 20-25 psi.

The original G250 guide specificed it be tuned just short of freeflow with the knob all the way out. I have also seen it recommended to tune them to to the 1.2 to 1.4" range with the knob 1 and a half turns inward. In practice the results are basically the same, just less precise on the all the way out end of adjustment.

An unbalanced schrader valve type inflator should not be failing at 165-170 psi (a high-normal 145 psi IP plus an extra 20-25 psi) but they do seem to start leaking and failing around 220-250 psi. A balanced inflator with no bias will probbaly not leak due to high pressure at all.

 

[Couv]

It's funny, I just pulled out my MK10 for a dive tomorrow and found the IP creeping steadily out of range after a few cycles on a full tank. I changed the seat (only had a used one) and the same thing happened. I then changed the piston (lucky me, I had a NOS piston sitting around) and problem solved, going back to the newer seat. The funny thing is that I recently bought the reg, rebuilt it and used it once without incident. Next step is to borrow a good strong magnifying glass and carefully check the knife edge on the piston I took out.

The reg came with a red, sort of translucent seal. I replaced it with one of the grey seals from a MK5 kit. I checked, and on my drawings the MK5 seat and MK10 seat are the same part number. What I hope is that I did not damage the piston in the MK10 by using a grey MK5 seat. I sure can't see any damage or feel any, but the magnifying glass will probably tell me for sure.

Matt,

The 5 and 10 do use the same hp seat. The last set of soft seats I bought were the gray ones. Incidentally, if you have an old white puck type you can just flip it. Also, in a pinch, you can lay a piece of sandpaper on a very flat surface and sand down the puck type seat until the piston grooves are removed. (Or so I hear )

If you really want to DIY, get a piece of teflon dowel and machine it to size.

c

 

[redacted]

That groove goes a ways into the HP seat so if you ever try refinishing the seat, you will probably have to add a thin shim between it and the retainer. I have taken some real light sand paper (like 400) to an LP seat on the older G250 style poppets just to test a used reg. But it really is much easier to just grab another seat, or better yet another reg. Plus removing an HP seat from the retainer almost guauranties you will get multiple overlaping grooves which compounds the problem. Better to live with a little creep until you can fix it right if it can be controlled.