What is PTFE?

PTFE stands for polytetrafluoroethylene which has the lowest coefficient of friction of any solid. It is used for coating non stick cooking vessels, and is used for low friction bearings. It must not be heated to high temperatures. If it is heated to high temperatures it gives off a highly poisonous gas.

PTFE can give good performance in some guns, but it depends greatly on the gun design and whether the cylinder is parallel etc.

Our washers are designed for low friction and a higher swept volume if possible. In most cases they are as easy to fit as the standard washer.

The main exception is the Original Diana models 45 and 50 T01 which uses a rivet to fix the main piston washer to the piston. The main piston washers on the older models were held on a screw. These were often found to have a rivet pressed in from the side to stake the screw thus preventing it from coming undone. See diagram A.

The Original Diana models with a dovetail fitting can be made easier to fit by slightly radiussing the sharp front edge to allow the washer to clip over without catching on the sharp edge.

PTFE Washers (Beware of Copies).

* Advance design features

* Designed for more swept volume

* High Quality PTFE materials

* Very low friction

* Requires virtually no lubrication after assembly

* Normally uses the standard washer fixture, with no modification.

* Eliminates Dieseling, if lubricated correctly

Fitting a PTFE washer

Please read carefully.

If the piston washer has a screw or nut fixing do not overtighten the retaining nut or screw, instead Locktite or similar threadlocking product should be used. Aim to get the screw or nut slightly recessed into the face of the washer. This will allow for bedding in.

The washers are normally made a couple of thou under size and a perfect air seal is achieved after a short "running in" period (usually within 500 shots) when the washer has sized to the bore of the cylinder.

This method is preferable to dry firing which can cause over expansion and frictional problems.

Never dry fire a spring air gun.

If on rare occasions the washer is a tight fit, you can benefit by wrapping 400 wet and dry around the washer, and with a back and forth motion while rotating, take a little PTFE off until a smooth fit is obtained.

For extra swept volume, PTFE washers are in some cases thinner than the standard washers to obtain more swept volume. And on some models protruding studs or screws may need to be shortened accordingly.

With the new washer in place, the gun should be inspected to make sure a small clearance remains between the rear of cocking arm and the rear of the piston slot. This is rarely a problem.

Degrease the cylinder completely before assembly. Follow the lube instructions sheet which is supplied when any of the Robb lubes are purchased, or see the Airgun Tuning Manual.

Fibre backing washers, if fitted with the original washer, should be used if the piston is a poor fit in the cylinder.

Finally, PTFE washers require one drop of MS 40 Silicon oil smeared around the piston head before assembly. But do not reapply until the next overhaul.

The HW 35 used to be fitted with a leather washer which was held on by a large nut. The Later HW35s are fitted with a polypropylene washer, the same as the HW 80 and 90. This type just clips over a lip, after peeling the old one off.

Made to fit 99% of all airguns.     





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