A NEW DEVICE AND HOW IT WORKS
Ed’s Introductory Note: Each new TC was issued with a little pocket sized booklet as per the scanned copy shown (it will be noted that mine has seen better days!). Inside my copy I found two inserts; one is a single sheet which gives hints on care and maintenance of Dunlop synthetic tyres, the other is a quarto size pamphlet of four pages (including front and back).
The front of the pamphlet has the MG Octagon and the Safety Fast! logo and a note in the bottom right hand corner, which states “The M.G. Midget “TC” Series cars are equipped with Hydraulic Dampers incorporating the “Pressure Recuperation” feature. This reprint from ‘The Light Car’ explains, in non-technical language, how they operate.”
The back of the pamphlet says “WITH THE COMPLIMENTS OF THE M. G. CAR COMPANY LTD.,” plus address, telephone number and telegraphic address. “PRINTED BY TEMPLE PRESS LTD., LONDON E.C.1” is in the bottom left hand corner.
The two inside pages of the pamphlet explain how the hydraulic dampers work and the re-printed article from ‘The Light Car’ starts with a sketch of a section of a double-acting unit.
Section of a complete double-acting unit, showing the cam-operated pistons, and the baffle (D) which seals off the recuperating chamber above it, except for a “pre-determined leak” past the extension of the filler cap (E).
“You’ve read a good deal already about the Luvax piston-type pressure recuperating shock-absorber in the descriptions of new cars that have appeared in “The Light Car.” What is it? What does the term mean? How does it work?
Well, first of all, you must forget the term “shock-absorber”; it is considered to be a misnomer: the road springs are the shock-absorbers. Damper is a better term. Next, an amplification of the name: the result is the Luvax-Girling Damper and that is the name by which this particular commodity will be known in future. We must stress the fact that it is an entirely new and improved version of our old friend the Luvax shock-absorber.
The secret of the Damper is wrapped up in the term “pressure recuperating”. In essentially non-technical language, this means that when the piston returns to its “neutral” position after its initial damping movement, the cavity thus formed in the end of the cylinder is filled with oil-completely filled-for the simple reason that the oil has nowhere else to go. This is important. The piston must be “fully armed” for the next damping stroke, and it can’t be unless the cavity or chamber is fully replenished.
Now let us see how it works, assuming, for the sake of simplicity, that there is only one piston (the double-acting type shown in the sketch has two opposed pistons).
Deflection of the chassis frame partially rotates an arm, one end of which actuates a cam. In turn, that cam forces a piston outwards in a cylinder. The speed with which the piston can move outwards, however, is governed by the speed with which oil can be transferred from one side of the piston to the other. This is controlled by (A) a relief valve and (B) a “bleed,” the area of which is fixed by a restrictor pin. Both valve and “bleed” are part of the piston. The “bleed” is formed by a small flat on the top of the piston and a hole through which the restrictor passes.
A section of one of the pistons. (A) is the relief valve. (B) is the “bleed” and (C) the disc-type recuperator valve. The curved member on the extreme left is a steel spring which keeps the valve assembly in place.
On the return or inward stroke of the piston (as the chassis frame rises again) a disc-type recuperator valve permits the oil to be quickly transferred back again to the other side of the piston.
The transference is complete, because the body of the Damper, which is of course, filled with oil, is sealed by a lid or (to give it its technical term) a baffle.
The baffle has one important peculiarity in the shape of a “pre-determined annular leak,” which does, in fact, permit oil to pass to the recuperation chamber above it. The leak permits a slow flow, but is too small to accommodate a rapid flow such as that which movement of the piston tends to generate. Its object is to take care of volumetric increases due to expansion by temperature and to permit the oil to pass back again to the main oil chamber when the temperature falls.
To sum up, then, the piston moves backwards and forwards, the displaced oil on one side being squeezed via the appropriate ports and valve into the space on the other side. The manner of its regulation governs the ease, and therefore the speed, with which the piston can move, and the operating arm of the Damper can oscillate. That regulation of movement provides the damping action which enables you to drive over bumps and potholes as though they weren’t there.
These Dampers are not adjustable. The best setting is obtained during actual road tests of each make (and model) of car and this setting is adopted on the standard production model.
The new Luvax-Girling Damper is good for 25,000 miles without attention. It is not an afterthought, so to speak, but an integral part of the springing assembly: a scientific device which is the outcome of much thought, knowledge and experiment: and it has a stern task, for pressures up to 1,000 lb. per sq. in. may be generated.
It’s nice to think that you haven’t got to worry about it, but it’s worth knowing how it works”.
Ed’s note: I rather liked the reference to being able to drive over bumps and potholes as though they weren’t there! The roads must have been in better condition in the 1940s than they are now.
I spoke to Derek Stevenson of Stevson Motors in Birmingham about reconditioning of dampers. His company, founded in 1944, has been reconditioning vintage and classic lever arm and telescopic types for many years.
Derek told me that the dampers are neglected for maintenance purposes on many cars with the result that sludge forms in them and blocks the valves. A split casing renders the damper un-repairable and new casings are not currently available.
Derek’s website is at www.stevsonmotors.co.uk. He also sells flexible steel braided fuel hoses, brake hoses and brake pipes and accessories.