smallbrother
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Post by smallbrother on May 14, 2021 8:05:48 GMT
I found one of the commercial safety valves was prone to buzzing. I'm sure I read about this on the SV info kindly sent to me but can't find it. Can anyone advise what would cause this please? Pete. The cause of buzzing is that the outlet holes to atmosphere are too small / partly covered by the spring generating back pressure in the body of the valve. This causes the valve to open and close at at a high frequency which is the buzz. In my own experiments to overcome this exact problem, I concluded the outlet to atmosphere must have an area equal to 150% of the valve bore. A valve of my own making had the buzz. I changed every possible thing (springs, seat types, clearances, everything) to no avail. I did the calc's. Outlet area was 130% from memory. Added one hole - in anger, with a pistol drill, while in steam - and problem solved! Since then, I have made many valves of different styles. It is a peculiar obsession of mine. I still stand by the 150% relationship. That's interesting! These valves are commercial and presumably made to the same specification. Only one had the problem. I have actually taken the buzzing one apart and somehow lost the bits. Ordered another. See how that goes. Pete.
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stevep
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Post by stevep on May 14, 2021 18:35:46 GMT
I found one of the commercial safety valves was prone to buzzing. I'm sure I read about this on the SV info kindly sent to me but can't find it. Can anyone advise what would cause this please? Pete. The cause of buzzing is that the outlet holes to atmosphere are too small / partly covered by the spring generating back pressure in the body of the valve. This causes the valve to open and close at at a high frequency which is the buzz. In my own experiments to overcome this exact problem, I concluded the outlet to atmosphere must have an area equal to 150% of the valve bore. A valve of my own making had the buzz. I changed every possible thing (springs, seat types, clearances, everything) to no avail. I did the calc's. Outlet area was 130% from memory. Added one hole - in anger, with a pistol drill, while in steam - and problem solved! Since then, I have made many valves of different styles. It is a peculiar obsession of mine. I still stand by the 150% relationship. Ross, I am not sure if Pete's problem is when the valves are blowing off, or when just under normal steam pressure. You are right that if the exit holes are too small, there will be issues when the valves lift, but if the problem Pete is seeing is when the engine is under steam but the valves are not lifting, then it is probably a ball not seating nicely on the seat.
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smallbrother
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Post by smallbrother on May 14, 2021 19:16:53 GMT
The cause of buzzing is that the outlet holes to atmosphere are too small / partly covered by the spring generating back pressure in the body of the valve. This causes the valve to open and close at at a high frequency which is the buzz. In my own experiments to overcome this exact problem, I concluded the outlet to atmosphere must have an area equal to 150% of the valve bore. A valve of my own making had the buzz. I changed every possible thing (springs, seat types, clearances, everything) to no avail. I did the calc's. Outlet area was 130% from memory. Added one hole - in anger, with a pistol drill, while in steam - and problem solved! Since then, I have made many valves of different styles. It is a peculiar obsession of mine. I still stand by the 150% relationship. Ross, I am not sure if Pete's problem is when the valves are blowing off, or when just under normal steam pressure. You are right that if the exit holes are too small, there will be issues when the valves lift, but if the problem Pete is seeing is when the engine is under steam but the valves are not lifting, then it is probably a ball not seating nicely on the seat. Sorry I should have clarified this before. The buzzing occurred before blowing off. So presumably the ball was not seating well. Let's hope the new one behaves itself. I assume if it happens again a whack to seat the ball would be in order. Pete.
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Post by steamer5 on May 14, 2021 20:18:02 GMT
Pete, Keep at it you'll beat it! Rather than whacking it use Rogers technique of getting a Silicon Nitride ball & giving it a squeeze to for the seat
Cheers Kerrin
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Post by Boadicea on May 15, 2021 8:36:19 GMT
Since the whacking technique was mentioned, I have tried the whacking technique, but I cannot recall when just whacking a safety valve or a clack, has improved its performance. I have seen others at a club "help" someone by doing it, and still never worked, but they did not have to take it home and fix it! As always, putting the time in and doing it properly is the only way. Probably not the right place to say this - I know Pete does not fall into this category.
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smallbrother
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Post by smallbrother on May 15, 2021 19:07:15 GMT
I did actually cure a leaking safety valve by seating the ball with a firm tap from a hammer.
Lots of experienced people advise this course of action.
Pete.
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stevep
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Post by stevep on May 16, 2021 10:01:22 GMT
I did actually cure a leaking safety valve by seating the ball with a firm tap from a hammer. Lots of experienced people advise this course of action. Pete. Hopefully, not when it was in place in the boiler!
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smallbrother
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Post by smallbrother on May 16, 2021 10:59:22 GMT
I did actually cure a leaking safety valve by seating the ball with a firm tap from a hammer. Lots of experienced people advise this course of action. Pete. Hopefully, not when it was in place in the boiler! Oh certainly not. Just imagine doing that! Pete.
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uuu
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Post by uuu on May 16, 2021 11:00:47 GMT
I thought it was the shovel you hit it with, whilst in the boiler.
Wilf
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millman
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Post by millman on May 16, 2021 13:06:47 GMT
You’re right Will, it is the shovel. Seen it done many, many times.
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Post by ettingtonliam on May 16, 2021 21:35:43 GMT
I think thats for non-pop safety valves when they just 'sizzle' after blowing off. A quick tap with the back of the shovel settles them down.
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