Another booster pump

[Joe Brancato]

If you guys need special parts, I know of sources. Just call me at the number below.

[rsterne]

Here is what I am thinking of for my Booster.... The shaded area is the top of the pneumatic cylinder....



You will note that there is a cup over the lower end of the cylinder, with a hole that just clears the piston rod (~ 0.003" clearance).... The O-ring that seals the piston rod at that end sits against the cup, and in a recess in the lower end of the cylinder.... I am thinking a # 214 90D O-ring (cross section 0.139") which has a nominal ID of 0.984", which is 25mm, with the recess in the cylinder being 1.240" in diameter, giving a squish on the O-ring of 0.011" per side....

I have 2 questions....

1. Would a quad seal be a better choice instead of a round O-ring?....
2. Can I simply use 3 or 4 x 10-32 set-screws in the cup, biting into recesses in the OD of the cylinder, to hold the cylinder in place?....

I don't want to thread them together, as the headstock in my lathe has too small a throughbore to single-point the OD of the cylinder.... The way I see it, if the O-ring (or quad seal) holds, there is no end load on the cylinder, as it is open on the other end, the load is only on the piston.... My only concern would be if the O-ring failed and air leaked into the space between the cup and the end of the cylinder.... At that point, there would be a momentary load on the cylinder, forcing it out of the cup....

Al, what do you think?.... Is there any danger here?.... If so, what would you suggest?....

Bob

[Gippeto]

1. Would a quad seal be a better choice instead of a round O-ring?....
2. Can I simply use 3 or 4 x 10-32 set-screws in the cup, biting into recesses in the OD of the cylinder, to hold the cylinder in place?....

I don't want to thread them together, as the headstock in my lathe has too small a throughbore to single-point the OD of the cylinder.... The way I see it, if the O-ring (or quad seal) holds, there is no end load on the cylinder, as it is open on the other end, the load is only on the piston.... My only concern would be if the O-ring failed and air leaked into the space between the cup and the end of the cylinder.... At that point, there would be a momentary load on the cylinder, forcing it out of the cup....

Al, what do you think?.... Is there any danger here?.... If so, what would you suggest?....

Bob

Quad rings are good stuff, and will carry a little lube between the seals which gets distributed to sealing face a little each time the sealing face "rolls" under pressure. If you can get them local, have at it...would just use an oring.

IMO, there is going to be a thrust developed, but eh...I've been wrong before. I would calculate it as the area of the oring under pressure (1 1/4" od x 1" id... .422 in2) At 3000psi, considerable force..1266 lb.

If you can put your screws in shear...you know how to calculate that. A bunch of ways to handle it, some simple, some less so...you know the limits of your equipment better than any. Bolted flanges with a collar set into or brazed onto the tube, braze the cup to tube.... Pick something, run the numbers and make chips.


Think you've seen a picture of mine...HP end is built like a hydraulic cylinder...bolts handle the load in tension.



Al

[rsterne]

Silver soldering the cup to the tube might be the ticket, using Easy-Flo 45, strong like truck.... Thanks....

Bob