Excitement

[Doc Sharptail]

...A little too much of.

Finally got set up with a bank that does EMT. Way too much running around setting up accts and passwords.

...Then my +ten year old computer crashes.

Now no e-mail access.

At least I got another order rolling with Eric at scopes and ammo. Much thanks to him for being patient with all the questions- a class act, as usual. Now the wait begins...

Which brings me back onto topic

I've been reading a bit about the 78 series valve stem, and it appears they need replacing with delrin, for what I'm about to subject them to. Anyone know where to source delrin valve stems? Or am I going to be safe for a while with the factory stem, doing a slow work up to hpa performance?

The other concern is an rva. I had it in mind to make one. I don't have access to a lathe, and the drill press I've been using has had me doing the slow burn thing as of late. I'll probably play with shimming the hammer spring a bit first, but I'm likely going to want some measure of adjustable spring control. Wish I could spring for a mill table and lathe...

Life is good, though. I'm looking forward to the next few weeks.

Regards,

Doc Sharptail

[sholo]

I know how you feel Doc, with regards to setting up EMT, crashing computers and no email. I went through the exact same thing last year (in the same order too!). It just plain sucks! Glad you got it all straightened out...

As for the '78 needing delrin valve stems when running HPA, I've heard that too. Like you, I don't have a lathe/mill either so I contacted RVD over at the CAF a few months ago about getting one made up (him and Magnumair are apparently the "guru's" on QB's) but at the time he was out of material for making stems. He may have stock on hand now? Wouldn't hurt to drop him a PM to find out...

Are you going to use a regulated bottle, or an HPA tube @ 3000 psi? Reason I ask is because if using a regulated bottle @ 1500-1600 psi, you may be fine with the stock stem (for now, anyways). FWIW, I've been using the stock stem for about a year now running 1500 psi with no problems or inconsistency's whatsoever after roughly 2500-3000 shots through it. It may (?) fail at some point, but I will keep using it until then. Be interesting to see if/when it does conk out on me...My guess is that if it does fail, it will no doubt be in the middle of an FT match!

If you plan on using an HPA tube @ 3000 psi fill, I don't think the factory stem seal will hold up too long at those pressures as they were never designed to see that kind of force exerted on them. Hopefully someone (a lot smarter than me) will chime in with a more definitive answer for you...

Cheers,
Todd

[SeanMP]

Sounds like a great project Doc.. I wouldn't be concerned about the stock stem not holding up. Both Bob and myself have taken stock stems up to some fairly high Fpe's. I think the main idea behind the Delrin is slightly reduced mass allowing higher operating pressures and slightly smaller OD giving higher flow yields.
But I can report that a certain little birdie talked to a certain Airgun elf this week and these stems will be available soon

[sholo]

But I can report that a certain little birdie talked to a certain Airgun elf this week and these stems will be available soon

[Doc Sharptail]

I'm on one of the Dell re-furbs that XS Cargo had on last year for 99 and change. I got it for just this contigency, and I'm glad I did. I think all the enhanced security features that come with EMT accts scared the crap out of my old machine.

I have one of the hpa tubes Eric had on the site a while back. I can't see myself subjecting it to that 3K psi.
Ideally, I'd like to see it at a lot less than 1600 psi- hopefully somewhere between 1200 and 1500. Bottles and tanks and compressors and shoe boxes can come later. I'm not in that much of a hurry yet. As usual, everything done in small increments, with the learning curve. I've ordered the hill pump, and a few other goodies for the 78's.

Was playing with the MK-1 last night, and it needs a new piercing pin seal. Too bad I haven't won 649 yet- there's so much stuff I want to get.

Regards,

Doc Sharptail

[rsterne]

Since CO2 can reach 1900 psi at 120*F, and if you're running HPA on a stock QB tube you should be running a 1.8K burst disc to limit the pressure to 1800 psi (which means running 1600 MAX).... The stock stem seal will live OK, at least for a considerable length of time.... It will eventually extrude into the throat and choke off the flow a bit, and it will require a stronger hammer hit to unstick, however....

Having said that, I replaced the stock seal with a Delrin washer pressed into place in the stock poppet head and machined off flat.... and LOST a few fps.... so bottom line, using a Delrin head may be more about making the head a bit smaller and lighter than anything else....

Bob

[Doc Sharptail]

But I can report that a certain little birdie talked to a certain Airgun elf this week and these stems will be available soon

Great! Hope that includes the rva's...



Regards,

Doc Sharptail

[AirGunEric]

The idea with the Delrin-plunger stem, as Sean and Bob have pointed out, was for the purpose of size (flow) and weight. If staying below 1600psi, the stock valvestem should be fine.

[Doc Sharptail]

The Hill pump arrived today. I'm bed-ridden with a wicked stomach flu right now. Didn't stop me from assembling the pump and it's fittings hand tight.

It seems to be very well made- it's a lot bigger than what I was expecting. The gauge reads in both PSI and BAR, so that's a bit of a relief. I was worried I was going to have to calculate from bar...

I'll have to figure out some kind of a case for this thing. Primary concern is keeping it clean, and protecting it in the back of the van.

I hope I'm feeling well enough in the morning to switch over tubes, and try building up a little pressure in the 78. If I'm lucky, saturday will see me out trying to shoot.

I also ordered in another 20-78-A stock. Apart from a few slight wrinkles in the finish, it looks pretty good. I'm really looking forward to getting all these 78 projects out of the way. Which reminds me, I have a .177 QB bbl here, and will have a spare tube... almost enough to start another rifle all I'll need is a trigger group and guard,hammer and spring, assorted cocking pins etc., and a .177 bolt and handle...

Big thanks to Eric for his help getting this order together. Fastest turn around time yet, only 3 days.

Regards,

Doc Sharptail

[sholo]

Congrats on your new arrival, Doc ....you are pretty well set up for HPA now, right? Let the fun begin!

You probably already seen this before (or knew this already), but in case you didn't, Eric posted this link awhile ago regarding maintenance of your Hill pump. Handy to have: http://www.airriflepump.com/downloads.html I've had mine for close to a year now and never any problems with it. Periodically apply a light smear of silicone grease on the pump tube, don't let it get too warm while pumping and change the dry-pac granules every couple months is basically all that is needed to avoid problems.

Hope you are feeling better soon. Everyone here at home had that bug a few weeks back and it knocks the sh!t outta you - both figuratively AND literally!

Todd