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How to Fit a PTFE Washer

Fitting a PTFE Washer!

PTFE stands for Polytetrafluoroethylene and this is sometimes used to coat non stick pans. It reduces friction and wear, so will reduce energy consumption, i.e. more efficient use of available energy.

PTFE Washers require a round and parallel cylinder, surprisingly a lot of guns do not have this, and some may taper at the bottom of the stroke (this is caused by the brazing process that shrinks when the cylinder cools). If the cylinder has a taper at the bottom, it will size the washer to this smaller diameter. Then when the is cocked, the washer will be a loose fit and allow air to escape when the gun is fired. This is why PTFE can work really good in some and really poor in others. For best performance check that your cylinder is round and parallel. Even high quality guns can have poor cylinders. If the cylinder is poor then the standard flexible washer may work better, if it has one. Some of the older guns are fitted with a leather washer, but these are prone to dieseling unless lubricated correctly.

PTFE Washers have very low friction, so when fitted properly can give the gun a bit more power for a given spring energy. Fitting a spring that is too strong will give the gun excessive recoil that will generally spoil the accuracy.

Our washers are usually made slightly smaller than the bore by about one to four thousandths of an in inch to allow for bedding in.

PTFE Must not be heated too high or it may produce a poisonous gas. It can give good performance in some guns. This depends greatly on the gun design and wether the cylinder is parallel and round. If you use a bore gauge I think like me you would be surprised how even a relatively high quality gun is out of round or tapered. Also bores on some guns can vary by quite a lot from one gun to another.

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 or RWS model 45 and 50 T01 that uses a rivet to fix the main piston washer to the piston. The main piston washers fitted on the earlier guns  were held on with a countersunk screw, (some have a side pin pressed in to prevent it working loose). Some of the later guns like the Original 52/54/38/34/and Air Arms TX200 have a dovetail fitting. The fitting of these can be made easier by putting a slight radius on the front edge to allow the washer to clip over without catching on the sharp edge. Some can be cut diagonally and fitted like a piston ring.

If the piston washer has a nut or screw fixing, do not over tighten the retaining nut or screw. Instead use Locktite or similar thread locking compound. Aim to get the nut or screw slightly recessed into the face of the washer. This will allow for bedding in.

Our washers are normally made a few thou under the bore size and a good seal is achieved after a short running in period, usually within 500 shots when the washer has sized itself 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 piston airgun.

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

For extra swept volume, my 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 shortened accordingly.

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

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

Fibre backing washers, if fitted should be used to support the washer. The fibre backing washers are used when the pistons are a poor fit in the cylinder. We have now made some of the fibre backing washers and these can be purchased for £1.50 with the PTFE washer.

For the old mark 1 and 2 Airsporters, that have a leather washer with a nylon core, there are two types of these washers,  on one the nylon formed part of the cone and the other one the nylon did not form part of the cone. We make both types but need to know which type you have.

A lot of the plastic seals disintegrate after a while, so it is worth replacing after five to ten years. See Photo. This was a washer that was fitted to a Feinwerkbau Sport.

The guns with plastic washers that suffer are:

Original/Diana/Feinwerkbau/BSA/ and others that have a plastic washer. This also applies to the breech seals.

PTFE Washers, Seals and Valves. We also make and sell Seals from many types of materials for Pre-Charge, Spring, Single Stroke Pneumatics, Multi Stroke Pneumatics, Co2, and most of the rest of guns.


We make PTFE Washers for nearly all Airguns, including obsolete ones. We also make Heavy Duty Breech Seals.


PTFE Washers (Beware of copies).

1    Advance design features


2    Designed for more swept volume (if possible)


3    High Quality PTFE materials


4    Very low friction


5    Requires virtually no lubricant after assembly


6    Normally uses standard washer fixing, with no modification


7    Eliminates Dieseling, when lubricated correctly