Offered here is a Chapmen hydro aspirator vacuum filter pump.  This unit is manufactured in the U.S.A. by Humboldt. The Chapmen aspirator is designed for greater air entrainment capacity and will perform under both high and low water pressure conditions.  The pump features a ball-type positive action valve in the suction tube which will prevent water backflow if the pressure is reduced. The body is a nickel plated white metal and the baffle tube is manufactured from aluminum.  The water inlet connection thread is a standard 3/8" NPT taper. Specifications:   Vacuum Inlet:  10 mm / .385" Water Outlet:     10 mm / .385" Length:   137 mm / 5 3/8" Vacuum generated  @ 30 psi 29.5" Hg At a water pressure of 30 psi this aspirator will reduce atmospheric pressure by 29.5" Hg. Standard pressure 29.92" Hg  = 1 atm                           - 29.50" Hg  Net pressure =       0.42" Hg  = 0.014 atm The actual vacuum attained with this pump is directly proportional to the water pressure and current barometric pressure! Therefore, the amount of vacuum can be varied by adjusting the water pressure.  This pump can be used for siphoning, vacuum filtration and indirect fluid transport.    Also available is a short  vacuum hydro aspirator with a serrated tail and side arm. Click for a Short Aspirator