# Inline valve

Joined: September 25th, 2006, 2:19 pm
I think Ron Burnett did similar with air spring versus washers.

Could such work? If so, with maybe more options than locating spring washers at piston head?

Joined: November 28th, 2007, 12:42 am

Using rounded values, let's run thru a few calculations. The dimensions of the pneumatic spring:
overall volume                2.2 cu.in.
bore                               .93    (.18 valve stem)
length                             3.4
cross sectional area      .65 sq.in.
During the pump stroke, the pressure in the reservoir rises from 925 (the precharged value) to 1000. The displacer piston is moved .28 in. in the process of forcing in the ~12 cu.in. of air. During firing, and assuming adiabatic expansion, the reservoir pressure drops to 895. So......the force exerted on the piston, from start to finish goes from 650 lb (1000 x .65) to 582 (895 x .65). The effective spring rate, K (change in force/change in length), for this configuration is 245 lb/in. Since maintaining high cycle pressure is our goal, K should be kept small.

What can be accomplished with a mechanical spring within the same geometric outline? From a Schnorr catalog, #009100 fits our requirements of max force and OD. Listed values of 660 lb @.016 deflection and initial height .081 will work. The length of space available, after the pump stroke, is 3.12 in. and 48 springs [3.12/(.081-.016)] will fill it. Assuming a linear relationship between force and deflection, the spring rate for such a stack would be 840 and the generated pressure would go from 1000 to 640.

Comparing average cycle pressures for the first part of  the overall expansion process........950 vs 820. The spring stack would weigh .8 lb and cost upward of \$50. Hope this helps.

Ron

Joined: April 28th, 2010, 12:23 am

Joined: September 25th, 2006, 2:19 pm
Using rounded values, let's run thru a few calculations. The dimensions of the pneumatic spring:
overall volume                2.2 cu.in.
bore                               .93    (.18 valve stem)
length                             3.4
cross sectional area      .65 sq.in.
During the pump stroke, the pressure in the reservoir rises from 925 (the precharged value) to 1000. The displacer piston is moved .28 in. in the process of forcing in the ~12 cu.in. of air. During firing, and assuming adiabatic expansion, the reservoir pressure drops to 895. So......the force exerted on the piston, from start to finish goes from 650 lb (1000 x .65) to 582 (895 x .65). The effective spring rate, K (change in force/change in length), for this configuration is 245 lb/in. Since maintaining high cycle pressure is our goal, K should be kept small.

What can be accomplished with a mechanical spring within the same geometric outline? From a Schnorr catalog, #009100 fits our requirements of max force and OD. Listed values of 660 lb @.016 deflection and initial height .081 will work. The length of space available, after the pump stroke, is 3.12 in. and 48 springs [3.12/(.081-.016)] will fill it. Assuming a linear relationship between force and deflection, the spring rate for such a stack would be 840 and the generated pressure would go from 1000 to 640.

Comparing average cycle pressures for the first part of  the overall expansion process........950 vs 820. The spring stack would weigh .8 lb and cost upward of \$50. Hope this helps.

Ron

I believe I have absorbed it.

So your air spring was actually in cartridge form?

Joined: February 17th, 2010, 3:30 am
I think Ron Burnett did similar with air spring versus washers.

Could such work? If so, with maybe more options than locating spring washers at piston head?

of the spring loaded piston, and the advantage?.... By "blow open" stem, do you mean the stem is held closed by the trigger and opened by differential air pressure to dump the valve?....

I don't understand the basics of this design, I'm afraid....

Bob

Joined: September 25th, 2006, 2:19 pm
maintain a higher overall pressure on the charge durring the firing cycle per stored energy in the spring.

You are correct that the valve spool is blown open by a diff pressure per the diameter differences as shown. Once the valve is cracked, the entire area of the face of the spool can then recieve total force of the compressed charge.

I did not show any plans for triggering or searing the valve spool against the force it will apply. There can be varied methods of accomplishing such.

Joined: November 28th, 2007, 12:42 am
I believe I have absorbed it.

So your air spring was actually in cartridge form?
is a good way to characterize it. Here's the back end showing the thumb button used to close the exhaust valve. Also visible are the threads that secure the whole assembly (5.7 in. long) into the upper tube.

[/IMG]

Here's the front, the end of the exhaust valve being visible. With the valve closed and the barrel locked into place, the conical tip enters the pellet skirt. No wasted space.

[/IMG]

Ron

Joined: February 17th, 2010, 3:30 am
maintain a higher overall pressure on the charge durring the firing cycle per stored energy in the spring.

You are correct that the valve spool is blown open by a diff pressure per the diameter differences as shown. Once the valve is cracked, the entire area of the face of the spool can then recieve total force of the compressed charge.

I did not show any plans for triggering or searing the valve spool against the force it will apply. There can be varied methods of accomplishing such.
Bob

Joined: September 25th, 2006, 2:19 pm
is a good way to characterize it. Here's the back end showing the thumb button used to close the exhaust valve. Also visible are the threads that secure the whole assembly (5.7 in. long) into the upper tube.

[/IMG]

Here's the front, the end of the exhaust valve being visible. With the valve closed and the barrel locked into place, the conical tip enters the pellet skirt. No wasted space.

[/IMG]

Ron

No waste except a smidgeon of pressure drop by the amount the valve spindle withdraws, Can't get any better than that, I think.

Joined: June 5th, 2006, 12:49 am
Or is it worth sacrificing a bit of pressure in a longer run-up to get higher opening speed,
because this would raise the 'mean effective pressure' in the most important stage of acceleration?
Obviously with a small air charge you can't use too much for valve operation, there'd be a sweet
spot with power drop off either side.