An Interesting Double-acting Air Spring
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Gradual Damping of the Shock and Rapid Damping of the Rebound Obtained by Using Non return Valves A SHOCK-ABSORBING device of .1-1 simple and effective design is the N.P. Double Air Spring, manufactured by the National Pneumatic Co., of America, and marketed in this country by G. D. Peters and Co.. Ltd., Windsor Works, Slough. The device comprises a piston working in a closed cylinder, the latter being fixed to the axle of the vehicle and the piston rod to the frame.
The piston rod is hollow and air is drawn through it to an internal air chamber in the piston. Non-return valves connect the air chamber with the cylinder, so that if the piston moves upwards air is drawn into the space below the piston, and vice versa. The piston is equipped with a pressureequalizing device, comprising a drilled cushioning plug on the lower side, whilst on the upper side is a non-return valve which incorporates a small by-pass, this being smaller than the bole in the cushioning plug.
B40 When the road springs are deflected, due to a road shock, the piston is forced downwards, thus compressing the air below it. On the rebound, the piston moves upwards, and the air above the piston is compressed with a similar cushioning effect.
Provision is made for the cushioning of the " shock" stroke to be relatively gradual, and that of the " rebound " stroke.. relatively rapid. When the piston is forced downwards, due to a road shock, a certain amount of the air compressed is allowed to escape through the hole in the cushioning plug and the non-return valve, the size of this hole being adjusted to pro
vide the required degree of cushioning.
On the rebound stroke the nonreturn valve closes, and the only escape for the air is by way of the small bypass formed in the valve. As the area of this by-pass is, as already explained, much less than the area of the hole in the cushioning plug, less air can escape, and it follows that a similar pressure will be generated in a shorter stroke.
It is claimed that, by the use of N.P. air springs, of suitable size, the stiffness of the road springs may be reduced by as much as 25 per cent. anti still carry the same load at the sPine deflection, A further feature claimed for the device is that it reduces rolling on corners, any tendency to roll being checked immediately at either end of the axles.
Four sizes are available with diameters of 4 ins. and 5 ins., and varying maximum and minimum distances between the brackets.