Tuning FX Impact Mk2/M3 - slower first shot - no reg creep - quasi-scientific analysis

[Seeker]

Yes, I applied Huma oring lube. It's very good viscosivity wise. However, it may wear out over time. The rod is albo polished to reduce surface roughness. It's always a balance between its roughness and its ability to keep the lube in place.

The valve works considerably better with that peek washer. Previously I had about 10m/s of difference of the first shot without the washer.

I will examine Viton in a day or two to check if any extrusion happened. I will also change Viton80 to NBR90 just for ease of mind. I think HNBR90 would be even better here.

This solution cannot be considered as production ready. It requires much more testing over time. However, the initial results seem to be promising. I will definitely explore it further. The other positive aspect is the fact that rod is stabilized in a better way. It is not that loose as in the original design.

If you want to play with this design here you have the washer dimensions:





They slightly differ depending on the viewing angle - not ideal ideal measuring method. However, it should give you some rough idea. Just treat them as some baseline. Every rod and plug bore may have some differences and we talk about snuggish fit. I had to reduce the OD, enlarge ID and reduce thickness a little for a perfect fit. It is important to make sure the orings do not obstruct the plenum replenishing hole. All this fine tuning was done with some abrasive paper and a hand drill to make the washer spin.

I really treat that peek washer as a backup oring preventing the sealing oring from extrusion.

If you decide to play with this design you make it on your own responsibility as we deal with high pressures here.

It seems that FX has some low hanging fruit here. It's up to them if they decide to do their part.

 

[mubhaur]

Seeker Nice work I like to here the good news so far 

Mubhaur is that in your raw with Royale design balance valve ?

Yes with Royal design valve. Otherwise just a few fps up or down.

Bhaur 

 

[mubhaur]

These pics show the valve design of my modified RAW base on Royal style valve. 

Looks like some similar issue with the O ring extrusion etc.

What remedy do you suggest friends?

I didn't use any 70 shore overlap O ring and this 90 shore O ring is also a bit loose fit in tge cavity. 

Should I change the design and make a groove for the 90 shore O ring or some other advice please?

Bhaur

 

[mubhaur]

There is one thing that comes to my mind. If its not the O ring of valve of my modified RAW, then it may be that I do not tune it just below plateau.

In fact I keep my reg pressure much higher than normally desired as sometimes I have to shoot heavy pellets or same pellets at more fps.

For that purpose my reg and hammer spring is normally not is perfect harmony. 

I mean my guns are not tuned the way we do them. Like achieving max fps with a given reg pressure and then loosen hst a bit to reduce the fps by around 10 to 15 fps.

If I tune my RAW in this way I might get better results in first 2 shots.

Still if there is any extrusion of O ring I will like to know and address it.

Bhaur

 

[Bigragu]

Good job, SEEKER!

 

[Airgunmann]

Mubhaur I would try some other orings and if that doesn't work may need to use a backer ring 

 

[corny]

There is one thing that comes to my mind. If its not the O ring of valve of my modified RAW, then it may be that I do not tune it just below plateau.

In fact I keep my reg pressure much higher than normally desired as sometimes I have to shoot heavy pellets or same pellets at more fps.

For that purpose my reg and hammer spring is normally not is perfect harmony. 

I mean my guns are not tuned the way we do them. Like achieving max fps with a given reg pressure and then loosen hst a bit to reduce the fps by around 10 to 15 fps.

If I tune my RAW in this way I might get better results in first 2 shots.

Still if there is any extrusion of O ring I will like to know and address it.

Bhaur

Possibly lowered by the plenum pressure will help if you have a friction issue.

tuning to the knee of the shot curve, isn’t going to fix that problem, however it may be less obvious.

 

[mubhaur]

I just found that my RAW valve O ring has extrusion / wedging issue.

I shall redo that part with tight clearance using peek.

I understand it will be resolved. 

Just need a time slot from my machinist. 

May be I need to make a complete part again to eliminate extrusion / wedging if the design of old part didn't allow. 

Thanks friends. 

Bhaur 

 

[Seeker]

Post some pictures of these orings. Mine looked like that:

 

[mubhaur]

Post some pictures of these orings. Mine looked like that:

I didn't take pic when I was inspecting. But it clearly looks like there is enough space for extrusion for O ring in my valve rod and the seating side of O ring. 

Bhaur 

 

[Vetmx]

Very interesting mubhaur. My gun is in pieces because it keeps mystifying me about something unrelated to this topic. I will probably build a Seeker bushing while it’s apart.

 

[PikeP]

Post some pictures of these orings. Mine looked like that:

Have any idea how much squeeze the o-ring is under? Its installed OD and the bore OD?

 

[Airgunmann]

Very interesting mubhaur. My gun is in pieces because it keeps mystifying me about something unrelated to this topic. I will probably build a Seeker bushing while it’s apart.

I book marked it and will be revisiting when I take it apart it is always something to add upgrade to it seems like lol I'll likely be making one to wether it will be for original power plenum or maybe a 720 power plenum upgrade when they are available for mk2

 

[Seeker]

Post some pictures of these orings. Mine looked like that:

Have any idea how much squeeze the o-ring is under? Its installed OD and the bore OD?

Valve rod: 3mm

Plug bore: 8mm

Sealing oring: 2.84mmx2.62mm

 

[PikeP]

2.84 ID? x 2.62 CS 

Assuming so, 2.84mm / 3mm = 94.5%, which gives 5.5% stretch.

2.84+5.24*1.055 = 8.52mm when installed going into a 8mm bore?



That sound right? Pretty standard fit.



Glad its working for you. Maximum breakout friction occurs (supposedly) around 300 hrs, so if you get little to no variation after sitting for a few days, you solved your issue! 

 

[Vetmx]

There is one in my gun right now. If no leaks tomorrow, I set the gun back to its best slug tune or at least try. Then I will let it sit for another 24hrs and see if anything improved. Those little suckers aren’t fun to build. Have to be very aware of the plenum recharge hole. I will test it for several days because I need to make sure my regs settle to exactly where I want them. Should have some solid info by this weekend.

 

[mubhaur]

Just talked to a technical guy and he advised that if the clearances and arrangements of the peek disk is very good, there is no need to use 90 shore O ring. Even 70 shore will work and may work better.

As per his argument, 90 shore is used here in order to overcome the issues caused by incorrect clearances which cause extrusion and wedging. 

I think Seeker may try it at some stage. 

Bhaur

 

[Seeker]

That's true.

Here you go:





It's in Parker Oring Book.

So we need to assume the cleareances should be much smaller because the rod moves in the same direction as the pressure works. Dur90 seems to be on a safe side.

 

[mubhaur]

That's true.

Here you go:





It's in Parker Oring Book.

So we need to assume the cleareances should be much smaller because the rod moves in the same direction as the pressure works. Dur90 seems to be on a safe side.

So the little the clearance the better. We just have to take care that the rod should not be tight enough in the disk hole that it could cause problem in quickly shutting the valve.

 

[Seeker]

Right. Too tight is bad. Too loose and you can have oring extrusion. Is should move pretty freely without too big cleareance.