Theoben / Weihrauch HW90 Gas Ram Charging Pump Kit – Slim Jim

Suitable for “HE” and non “HE” Rams. 1-BA, and Standard Schrader Valve threads.

DO NOT USE A DIVE CYLINDER. CHRONO AFTER ADJUSTMENT

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Some useful information from:  AirgunBBS Forum Thread 245395

• The “HE” models (HE will be stamped on top of the breech) run at 700-1000PSI, depending on barrel length, calibre and the condition of the gun. 800-850 is most common, but I’d suggest to start at 700PSI and work upwards. More than 1000PSI risks damage to the ram. If it takes that much to get 11+ftlb, then the gun needs new breech, piston and ram seals.
• The pre-HE models run with half or less of the “HE” pressure.
• What is “HE” and why does it need more pressure? “HE” = high efficiency.
• It needs more pressure because the later Theoben’s have a short stroke length of just over two inches, with a cylinder bore of just over an inch.
• The stroke of the piston on a 12 ft lbs Theoben gas ram is 2.6 inches “HE” or not. The diameter of the (dummy piston) or gas ram on the “HE” model is 1/3 of that of the earlier one and the pressure goes up from 300 psi non “HE” to 750 psi “HE”. To achieve FAC velocity the stroke is increased to 3.2 inches the eliminator has a stroke of 3.7 inches. All Theobens after TB 6000 are “HE”.
• If I go over the 12ft/lb limit I gently tap the valve with a pin punch about “PFFFFFFT” is enough. It takes a bit of practice to do without a “POP” and a cloud of oily air being evident.