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Manufacturers Secrets: Pump Design

Written by Drenchenator
Last updated on 2007-12-18


The pump limits the gun. All of the power of a good water gun enters through the pump and out the nozzle. But how much power could be inputted into a gun? The manufacturers like Hasbro and Larami were kind enough to leave small hints as to what pump forces they designed for. The following table has taken information about the pressures within a fully charged stock gun to extrapolate the maximum force needed to pump.

Gun Pressure (psig) Stroke (in.) Diameter (in.) Volume (cu. in.) Force (lbs)
SC 600 22 6 0.591 1.648 6.041
CPS 3000 22 7 0.596 1.953 6.137
SC 500 26 6 0.580 1.587 6.875
CPS 1000 23 7 0.623 2.136 7.018
CPS 1500 22 7 0.666 2.441 7.672
XP 110 40 6.75 0.578 1.770 10.487
XP 70 40 6.125 0.585 1.648 10.760
CPS 2000 45 5.875 0.640 1.892 14.490
XP 250 45 6.5 0.750 2.872 19.990
XXP 275 45 6.25 0.899 3.967 28.559
CPS 23 6.600 0.611 1.953 6.749
XP 42.5 6.406 0.703 2.564 17.449

The final two rows list the averages for CPS guns with the exception of the CPS 2000 and the XP guns. The CPS guns do not require nearly as much force to pump because their pressures are much lower. However, the XP guns do require much force to pump.

In a conventional APH-style design, the gun is limited by the pump. Taking the forces from the chart as the forces that the manufacturers believed suited users, we can see one thing: 1/2" PVC pumps can get higher pressures that 3/4" PVC. Some simple math tells us that a 3/4" pump can only generate up to 32.7 psig with this these limits; a 1/2" pump can generate 57.4 psig.

It seems that the manufacturers designed their air pressure guns to take on average about 18 pounds of force on the final pump. This fact can be vital when designing a gun.


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