SP MK 10 PLUS: please help ID

[Couv]

Re: #1....2 shims and a + seat, that surprises me that the IP is that low. After you verify with another gage, why not play musical springs with the #3 unit. You may have a weak spring in #1. One more shim would most likely only bring it up another 4-5 psi. I measured a number of hp seats, and they are not all the same even with in the same equal, minus, plus group, so just trying a different seat may help. As Awap said, shimming the seat will result in a lower IP, not higher. Now if you want to do something radical, you can try to sand the seat down a bit. Shave the side that interfaces with the seat retainer, not the piston. I used to sand down the old white hockey puck hp seats. Also, (like Awap said) don't forget to index mark the position of the seat and retainer.

By the way, I sent you a few 90 duro -010 o-rings, even a couple of the "high dollar" polyurethane ones....don't tell Awap and Matt....they paid for them.

Couv

 

[redacted]

Re: #1....2 shims and a + seat, that surprises me that the IP is that low. After you verify with another gage, why not play musical springs with the #3 unit. You may have a weak spring in #1. One more shim would most likely only bring it up another 4-5 psi. I measured a number of hp seats, and they are not all the same even with in the same equal, minus, plus group, so just trying a different seat may help. As Awap said, shimming the seat will result in a lower IP, not higher. Now if you want to do something radical, you can try to sand the seat down a bit. Shave the side that interfaces with the seat retainer, not the piston. I used to sand down the old white hockey puck hp seats. Also, (like Awap said) don't forget to index mark the position of the seat and retainer.

By the way, I sent you a few 90 duro -010 o-rings, even a couple of the "high dollar" polyurethane ones....don't tell Awap and Matt....they paid for them.

Couv

Careful with those o-rings. I have had some that seem to have dried out and crack (break) as I fold them up to insert them into the body. I went through my supply and some feel soft and supple (as much as a duro 90 can ) and others feel very hard. I have not had any problem with them working as long as they don't break during installation. Just for the hell of it, I have tried lubing some in storage to see if that has any effect. I did not have this kind of problem with Parker urethane o-rings so I may have to go look for a source for smaller quantities of those again.

I have also found that my Mk10s show a 5 to 10 psi difference (more when not using urethane o-rings) in IP as a function of tank pressure, That is the main reason I am switching almost entirely to Mk5s and Mk7s. The larger piston and more robust spring result in IP much less effected by tank pressure.

 

[Zung]

Careful with those o-rings. I have had some that seem to have dried out and crack (break) as I fold them up to insert them into the body.

I have a small bag of original SP o-rings in rainbow colors, in which there are 2 PU 010 for the piston stem; I also have one removed from a MK10 after a service. By feel, all of these are *A LOT* softer than the aftermarket Nitrile 90's that I have; the difference is not subtle at all.

These o-rings must be 20 years old, and they still feel supple. I wonder where SP got them from?

If you want to setup a group buy, please count me in.

 

[Zung]

... I suspect you could add one Mk20 shim between the seat retainer and the body to raise IP about 5 psi...

Right on, awap!

I just added 1 MK20 shim between the seat retainer and the body: IP is now 123 PSI, recovery is near instantanuous, with a 1" creep from 122 to 123; hard to tell, it's within the width of the needle, and could well be the settling time of the gauge itself, or the edge is cutting a new groove.

I turned off the air, and the IP held for over an hour, so it's not leaking.

The theory is: there's an 013 o-ring (or a washer) between the seat and the body acting as a face seal; while the o-ring itself is spec'd at 1.78mm +/-.08mm, the nominal amount of compression is unknown. Adding a .3mm shim is stretching it a bit, but it works.

I'm getting there, slowly, just 2 PSI short of specs, but, as mattboy said, I can live with that happily ever after.

Now that my stash of shims is depleted, can we start talking about DIY shims, please?

 

[DA Aquamaster]

I have also found that my Mk10s show a 5 to 10 psi difference (more when not using urethane o-rings) in IP as a function of tank pressure, That is the main reason I am switching almost entirely to Mk5s and Mk7s. The larger piston and more robust spring result in IP much less effected by tank pressure.

In both the Mk 10 and Mk 5, the piston is straight with no flare toward the knife edge/orifice end as is found on the later Mk 20/25 pistons. This means the area ast the outside of the orifice is the same as the area of the stem passing through the HP stem o-ring. This means the actual area of the orifice itself is left unbalanced. That will result in a 4-6 psi difference in IP as tank pressure drops. (I have a chart somewhere that shows the theoretical drop with both Mk 5 and Mk 10, but it's not worth the time it takes to look for it.) The drop will be slightly less with the Mk 5 as it uses a larger diameter piston head, so less IP change is needed to accommodate what is essentially an identical change in downstream force with both the Mk 5 and Mk 10 due to the less than perfect balancing. But there will still be some change in IP with the Mk 5.

I have a small bag of original SP o-rings in rainbow colors, in which there are 2 PU 010 for the piston stem; I also have one removed from a MK10 after a service. By feel, all of these are *A LOT* softer than the aftermarket Nitrile 90's that I have; the difference is not subtle at all.

These o-rings must be 20 years old, and they still feel supple. I wonder where SP got them from?

If you want to setup a group buy, please count me in.

THe newer 90 duro o-rings are much harder and are slightly more difficult to install. The stiffer material was intended to reduce issues with the HP stem o-ring getting pinched at higher service pressures. With the older polyurethane o-rings it was not uncommon to encounter o-ring pinching and cutting at pressures over 3000 psi in Mk 10's with tolerances between piston stem and reg body that are on the generous side. It's much less of an issue with 90 duro o-rings.

 

[Zung]

... why not play musical springs with the #3 unit...

Done that, my brother, before the MK20 shim stunt: 117 PSI with the original spring, 110 PSI with the spring from the #3 unit, so I swapped back.

But now I'm cool with 123 PSI.

Thanks.

 

[Zung]

... I have also found that my Mk10s show a 5 to 10 psi difference (more when not using urethane o-rings) in IP as a function of tank pressure...

I wanted to do a test in this regard; the problem is I've been messing with 6 reg's this weekend, and 1200 PSI is all I've got by the time I got around to this guy, so I don't know about the situation with a full tank.

Anyway, I used mattboy's secret receipe of turning off the air and purging until the desired pressure comes up (I think it's mattboy; there're so many great ideas from this board I'm having serious issues tracking credits, my apologies if I goofed again). The IP holds up steady from 1200# down to 435#, starts drooping to 119 PSI at 290#, and 96 PSI at 145#. Sorry about the weird numbers, it's 80, 30, 20, and 10 bars over here.

 

[redacted]

I wanted to do a test in this regard; the problem is I've been messing with 6 reg's this weekend, and 1200 PSI is all I've got by the time I got around to this guy, so I don't know about the situation with a full tank.

Anyway, I used mattboy's secret receipe of turning off the air and purging until the desired pressure comes up (I think it's mattboy; there're so many great ideas from this board I'm having serious issues tracking credits, my apologies if I goofed again). The IP holds up steady from 1200# down to 435#, starts drooping to 119 PSI at 290#, and 96 PSI at 145#. Sorry about the weird numbers, it's 80, 30, 20, and 10 bars over here.

We have bars over here too but I think they are more enjoyable than your bars.

BTW, I assume ' is minutes and " is seconds.

 

[Zung]

... Plus, unless you are 100% certain your IP gauge is accurate, it may be higher...

The gauge is an El Cheapo, but the dial says CL 2.5, which I assume to be 2.5%. More importantly, the range I covered this weekend goes from the rogue #3 MK10 at 150 PSI through the in-specs MK20's and #2 MK10 Plus at 130 to this one at 120, so it makes at least some sort of "relative" sense.

Over here we have a product called micromesh that's a set of adhesive cloths ranging from 1500 to 12000 grit; it's designed for taking scratches out of acrylic.

I've been asking around but nobody knows about micromesh around here. awap told me about Brasso, and I managed to find a local equivalent; while it works something wonderful on brass, stainless steel seems to ignore it completely. I made a 5' attemp on a MK20 piston shaft, but it made no difference at all. Should I try longer?

 

[Zung]

We have bars over here too but I think they are more enjoyable than your bars.

Oh, I thought yours were called "saloons".

' is minutes and " is seconds.

Yessir, maybe I should spell them out in full.