Simple Valve Lift Indicator

[rsterne]

I have received some requests about how a Valve Lift Indicator is made and what it looks like.... This one is for a Disco, but the concept can be made to work with pretty much any PCP, pumper, or CO2 gun with a little thought.... Here is a photo....



I took a piece of 1/8" aluminum rod (to keep the weight down), threaded the end 5-40 (but turned/filed down and threaded 4-40 would work) and threaded on a thin nut and peened over the end of the rod.... The nut I chose was about the same thickness as two turns on the RVA, so you have to allow for that in your adjustment.... The nut is captured between the spring and the inside end of the hole in hammer and held in place by the spring.... You need a (loose fitting) hole in the rear spring seat (end plug or RVA adjusting screw) for the rod to pass through, and it has to be long enough to protrude through the end of the screw/plug when the gun has been fired, plus at least 1/4".... You then slide a 1/8" ID O-ring over the rod, it will be a friction fit, able to slide and yet stay in place....

When you cock the gun, you slide the O-ring forward a bit (it doesn't need to be rght against the screw/plug as the hammer travels quite a bit).... When you fire the gun, the hammer hits the valve and continues to travel as the valve opens.... The O-ring is pushed back by contact with the screw/plug and stops when the valve is at maximum lift.... The hammer, carrying the indicator, rebounds, and there is then a gap between the O-ring and the end of the screw/end plug.... That gap equals the amount of valve lift.... If you are concerned that the O-ring may have "stuck", or reduced the hammer strike, simply cock and fire the gun again to make sure it doesn't more further.... You can measure the gap with calipers, or using feeler gauges.... either way you have to be careful not to bump the O-ring or you will not get an accurate measurement.... When the gun is fired it looks like this....



The first time you do this, you will be amazed at two things.... 1. how little the valve opens.... and 2. that the valve opens about twice as far at the end of the shot string when the pressure is low than at the beginning when the pressure is high (in an unregulated PCP).... You will actually be able to SEE the self-regulation of the valve occurring.... Incidently, you can probably use a long thin Common Nail (such as a box nail) for the indicator rod, capturing the head of the nail under the spring.... It will be a bit heavier, but will still give an indication of what is going on.... The lighter the indicator assembly, and the thinner the head, the more accurately your measurements will compare to the way the gun operates without the indicator in place.... If you have a rear cocking hammer (or a full length spring guide that slides with the hammer) and put the O-ring on the cocking rod / guide, you are only adding the O-ring itself, so the results will be completely correct....

Bob

NOTE: this post is a duplicate of that in the thread on the bstaley Disco, but I thought it deserved a stand alone thread to increase exposure to those who may not be interested in that thread.... RBS

[FuzzyGrub]

Being one of those inquiring, thanks. 

[tobar832]

Bob,
   By finding your valve lift during your firing cycle say 2500psi to 1500psi how can I use this info?  Does it just help in the Bstaley tune or can I use it in tuning any PCP?  One other question, do you think the Bstaley method would help the tune of a B-50/51?
    I am going to try this on the B-51 just to see the lift on the Bam.
Thanks in advance,

Bill

[rsterne]

It's more of a curiosity than anything else.... although the imformation was extremely useful in determining how much travel a bstaley tune might need from one end to the other for travel on the striker.... If you find anything significantly less than 0.050" or more than 0.150", please let me know.... So far that covers all USEFUL lifts I have seen over a wide range of guns.... I have seen lifts over 0.150", but only when the hammer strike was wayyyyyyyy too much for the pressure, and hence the gun was operating in a VERY inefficient realm....

Bob

[tobar832]

When I get some data I will post for sure.  Anytime I can learn about the inter works of these guns it's worth the time to me.  This kind of discovery just makes AG more fun and interesting.

Thanks,
Bill