Reply To: Foster fitting problem??

Forums PCP Airguns Foster fitting problem?? Reply To: Foster fitting problem??

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steve-l
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Those Foster fittings one-way function depends on air pressure in the tank to seal. There is a simple cylindrical plug with a tiny O-ring on it just pressed into the fitting bore. To take it apart, all you need is a pin punch applied to the filter and push. Piece of cake! Now here's the tricky bit. Most of these have 1/8 BSPP (British Standard Pipe Parallel) threads, but not all. BSP threads use a 55 degree thread form, not 60 like metric or our National Standard threads, that's first. Secondly, these BSPP fittings seal on the base with a nylon washer, not on the threads with tape or sealant. If they are over torqued when assembling, the nylon washer will crush and squish out into the center hole interfering with the foster fitting's slug's motion potentially blocking the fitting from opening. So be careful tightening these fittings! By design, this fitting will not flow air without a positive pressure differential between the input and output side of the fitting. When the pressure in the tank is greater than at the input side, the tank pressure pushes the tiny slug through the fitting bore until the slug contacts the internal machined shoulder stopping its travel…….just sayin!