SP MK10 PLUS 1ST GENERATION.....?

[Mobulai]

I am kinda following, but.. why am I not seeing any pictures?
(also extrapolating a bit from the 2nd stage orifice diameter disparity)

 

[CG43]

If the piston sealing edge diameter is just a little bit bigger than the piston stem diameter at the o-ring, the IP will increase with lower IP.

If you manage to produce a piston with an equal diameter at the piston stem at the o-ring and the sealing edge, the IP should be equal at full and near empty tank, at least in theory.

Thats all right except the last word of the first sentence should be tank pressure .

There is a method of calculating the actual diameter of the sealing edge from the change in IP when the tank pressure changes.
First calculate the uncompensated defect area = Af
Then you can use this area to calculate the diameter of a orifice = D or in a non-compensated configuration, or the effective diameter = Dg of the annular ring area in a flow through piston stage.

Mit Ap = piston area
delta IP = change in IP
Af = not compensated area
delta t = change in tank pressure
D o = diameter O ring
pi = 3,14159

because of : Ap * delta IP = Af * delta t results : Af = Ap * ( delta IP / delta t )
D or = ( 4 * Af/pi ) : Dg = ( D o^2 - 4* Af/pi ) ^1/2

The orifice of a non-compensated 1st stage has a diameter of about 2.7 mm.
With Subapro, the stem of the piston has a diameter of about 6 mm on the outside.
You can quickly calculate how much smaller the sealing edge can be until you have the same drop in IP as with a non-compensated stage.