The valves in the Hutchwilco Fenders can be easily damaged if you use a needle style pump nozzle on them.

Repairing/replacing them is fairly easy though.

You will need:

A M3 bolt will thread into the top of the valve and give you something to grip with the pliers. The valves are push fits and will pull out with a bit of pressure.

Once the valve is out, look for a small spring that should be on the inside of the valve. This spring pushes the inner workings of the valve back into place and holds it shut. If it is not there, the valve will not close properly. If it is there, sometimes the valves corrode a bit, and a spray of some anti-corrosive lubricating fluid will free things up. 

You can test the working of the valve by using a small Allen key or punch in the top - the inner 'piston' should work free down and be pushed back by the screw.

In the above image you can see the spring has slightly come out of the end of the valve. Gently work it back inside.

Once the operation of the valve is confirmed, screw the M3 bolt back into the end and push back into the fender. Don't push it to far in. Flush with the opening is enough.