Like Robin I would question the need for Nitrile balls. I would use a steel ball to create the seat first even if using nitrile. The steel ball you use should be stainless. An 1/8″ is a very small ball – the portway will be way to small. I would think 1/4″ is more likely ? you have the drawings ? Noel.

I doubt PMR use metric balls and looking at this image I would say 5/32″ and 1/4″ are more likely based on the known 3/8″ pump ram. And looking elsewhere the drillings seem to be No29 (0.136″) and 7/32″ which would be about right for those ball sizes

On 30 November 2023 at 07:36 Martin Dare Said:

@robindufton

With a ball you mostly have edge contact, and I doubt that at these low pressure the seating surface will deform sufficiently to improve things.

You’re over thinking it. I’ve never known any issues anything like you’ve stated in my career to this point, as you don’t want the edge the ball sits on to deform. It needs to be a sharp defined edge. This is pretty much the passing boiler pressure relief valve and the hammer incident again, where it had to be explained to a junior engineer why we don’t hit valves with hammers.

Deep sea sailing vessels aside, on a model scale the Stuart feed pump I built had nothing like the issues you’re describing either. Every model check valve uses a steel ball bearing. You’re more than welcome to take a look at the feed pump I built and if you can reverse the flow through the pump, I’ll let you keep it.

On 1 December 2023 at 11:44 Martin Dare Said:

 

 

Useful tip, replace the potentially distorted ball after this exercise.

Flat.

On 1 December 2023 at 19:39 noel shelley Said:

It is a style of drill that drils a flat bottomed hole , or flattens the bottom of an already drilled hole. Noel.

So same as an centre-cutting endmill, although I wouldn’t want to use one to drill a hole from scratch, especially if it really was reground from a normal twist drill.

Ian P

On 1 December 2023 at 12:29 Neil Wyatt Said:

Useful tip, replace the potentially distorted ball after this exercise.

It isn’t. It’s creating a ball shaped recess for the ball to sit in and means there is more chance of something getting trapped, which will make it pass. If it’s a sharp edge anything that does get caught it’ll either cut it in half or it will have less oppotunity to get trapped in the first place. By hitting it with a hammer you’re basically doing the same as drilling it with a normal twist drill and having the ball sit in that cone.

Make the parts correctly in the first place, as I’m pretty sure Parker don’t have someone at the end of their production line hitting things with hammers. That or they have a machine to do it.