P-Rod hammer bouce from air compression?

[lloyd-ss]

I was working on a high powered modification to a P-Rod valve, the kind where air consumption is subordinate to power.
The valve and gun had these mods:
T-port opened to .125".  Stock T-port is .080".  Stock barrel port is already .125".
Exhaust port on valve opened to .125" and contoured for better flow.
Valve throat opened from .201 to .219.
Inside of main valve body back-bored to open the I.D. up approx .062 larger in the vicinity of the valve head for about .40" of length.
Return spring seat and valve moth opened up as much as possible.
Different return spring used that provided less  air flow blockage from its coils.
Valve stem shortened approx .020" to get a tiny bit more valve stroke.
Hammer spring changed to a .041 wire Disco aftermarket spring.

I am sure these mods are old news to many P-Rod owners and builders, so no big deal.

But I did notice one more thing this time that I hadn't noticed before.  Somebody might have already mentioned this and presented something about it, I don't know.

What I noticed was that before the hammer strikes the valve stem it runs past the ends of the slots in the air tube and compresses the air ahead of it just like a piston would do.  The compression distance is only about 1/8", and it slows the hammer a little bit.  But probably the worst thing is that it might promote hammer bounce from the rebound of the "air spring" that is created.

Since this was a high powered mod, I didn't want to leave anything un-done, so I drilled a small 7/64" hole thru the air tube at the back edge of the valve to give the air a place to escape.  The hole dumps the air into the slot in the top of the pistol grip.  It is slightly offset to line up with that slot.  Calculations show that there is still plenty of safety margin in supporting the screw head of the valve attachment screw.

Here are the pictures of the mod.

There is about 1/8" of compression before the hammer strike, and then up to another 1/8 with the valve stem travel.
 

Deburring the new hole inside the air tube is the hardest part. This hole also gives a quick escape route for any blow-by from around the valve stem.


Unfortunately, I did not test the valve before drilling the hole, so I do not have  before-and-after shots to show if the mod made a difference. But here are two of the max power shots at about 2900 psi.
28.4 gn EunJin  734 FPS, 34.0 FPE
21.3 gn H&N Barracuda  803 FPS, 30.5 FPE

Those are the most powerful shots I have ever had with a P-Rod with stock 12" barrel.
Like I said, this might be old news, but it is still cool.
Lloyd
 

[Hobbyman2007]

Lloyd,
Wouldn't the slots cut into the hammer allow any built up air to escape ? I've been using the prod grip frame and hammer on a couple discos ,would this be a reason for a large ES ?

[lloyd-ss]

Lloyd,
Wouldn't the slots cut into the hammer allow any built up air to escape ? I've been using the prod grip frame and hammer on a couple discos ,would this be a reason for a large ES ?

Ha, ha, egg on my face.  Right you are. The drilled hole is a totally unnecessary mod for the P-Rod.  Thank you.
But on the Disco, with the standard hammer, possibly.

[rsterne]

reaches over and scrapes off the egg.... 

You are correct about the Disco having the possibility of building a bit of pressure between the valve and hammer from compression (or blow-by from the valve stem).... The Disco valve is longer than the 22XX valve at the back, and NEARLY covers the vent hole in the bottom of the tube, which was placed there in the 22XX tubes (and for some reason still there) to avoid that problem (at least I can see no other reason for it).... My solution is to grind an angled notch in the back of the Disco valve to allow the air to easily reach that hole....



In that photo you can see the two notches in the back of the valve.... The one on top is to clear the front screw location in a 22XX breech, and the wider one, on the bottom, is to allow air to vent through the hole behind the lower screw hole....

Bob

[FuzzyGrub]

Lloyd,  Keep an eye on the cocking lug hitting the end of the slot.  When I was trying to get some extra stroke from the prod, via recessed striker, I noticed that was close to hitting. 

[screwwork]

Nice numbers Lloyd 
The Prod has some power in it for sure. Did you feel a puff of air from the hammer? JK

Here is what  did to my Prod valve.
My main problem is I opened up the Valve exhaust, transfer port and barrel port all the way up from .150, .160 and to .180 before opening up the Valve poppet id & throat id first. Live and learn!

Valve throat to .260(which was overkill)! .250 dia about 100% for 22 cal.
Rear Valve ID .390 to poppet seat
Front valve body is .390 except for the spring counter bore which is .281
I didn't have the fancy taper spring thing, so I Oakie rigged it so it wouldn't slip though the .281 hole.
.045 hammer spring .3 x 1.5"
With those mods this Prod valve is capable of 40 fpe for 5 shots easily and pushing it to 7 shots. I have it on You Tube LOL.. 

Opening up the rear valve body to .4 id is a great idea and gives up 100% of the poppet dia and using a better tapered spring for the inner valve spring.
I was thinking of trying to opening up the rear valve body to about .5 dia x .4 long for a little more but I don't think you'll get much more power out of the valve because of the valve design.  The other thing I would like to see is have a new front valve body that uses a shallow counterbore for forward trigger mounting screw. this way you could open up the body to the full .4 dia all the way back to the rear valve body. The only area that would be a smaller ID is the 2 valve to breech mounting screws that we cannot get a way from. 

Let me know what you think?

Thanks Randy

[Motorhead]

Lloyd,
Indeed your correct with a Double hand slap too 
Upon valve cracking open the Stem to body will LEAK and a small amount of HPA will enter the space between valves body and hammer ... further raising the pressure within the gap driving hammer back harder than it would by poppet reset energy alone 

Venting BOTH sides of a hammer is always a prudent effort when low ES figures & consistency is on the table 

[Buldawg76]

Following her as well

Mike