JohnDK
Active Member
Northampton SME member
Posts: 15
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Post by JohnDK on Mar 19, 2019 20:35:22 GMT
I am having a bit of a fight with sticking stainless steel balls in hand pumps and axle pumps in two 5 inch engines.
They seem to get stick after a very few weeks of non-use.
I replace them with nice new ones from time to time.
Should I consider nitrile balls?
John
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Post by builder01 on Mar 20, 2019 9:14:50 GMT
I replaced mine with Viton and never looked back.
David
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Post by Roger on Mar 20, 2019 9:52:05 GMT
Alternatively, you could modify the pumps to prevent the balls from sitting on the seats when they're in the relaxed position. I've just drilled a cross hole below the ball and inserted a piece of 1mm O-ring cord in the hole. That keeps the ball about 0.2mm above the seat but it's easily deflected downwards as soon as there's any flow or air or water in the reverse direction. If the ball isn't allowed to dry out while sitting on the seat, it will never stick.
I'd also suggest switching to Silicon Nitride balls which are much harder and have better tolerances than the Stainless Steel balls that are typically supplied to Model Engineers.
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JohnDK
Active Member
Northampton SME member
Posts: 15
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Post by JohnDK on Mar 20, 2019 11:37:26 GMT
Thanks for those ideas David and Roger.
I think I'll try a change of material first before doing anything more complicated.
John
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stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Mar 20, 2019 16:14:24 GMT
John,
I am wondering what water you use. If there are any dissolved solids in the water, when the check valve dries out, the residue can cause the ball to stick.
On the advice of one of my FCMs, I now use the water I take out of my dehumidifier. I previously used the water from my wife's condensing tumble drier, but I found I left a waft of Lenor behind me when I went round the track!
I would also mention that, again on the advice of a FCM, putting hot water into the side tanks freed up a sticking valve. Something about differential expansion??
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JohnDK
Active Member
Northampton SME member
Posts: 15
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Post by JohnDK on Mar 20, 2019 23:11:29 GMT
John, I am wondering what water you use. If there are any dissolved solids in the water, when the check valve dries out, the residue can cause the ball to stick. On the advice of one of my FCMs, I now use the water I take out of my dehumidifier. I previously used the water from my wife's condensing tumble drier, but I found I left a waft of Lenor behind me when I went round the track! I would also mention that, again on the advice of a FCM, putting hot water into the side tanks freed up a sticking valve. Something about differential expansion?? You are correct about the hot water trick - I am an expert at that! John |
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