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Post by builder01 on Sept 18, 2020 23:04:03 GMT
I get my Viton balls from McMaster-Carr, a supplier in the U.S. I am sure there is someplace in the U.K. that can supply them. They are not exactly cheap, they are usually sold by the "each". The good news is that they work and can be an exact replacement for a stainless ball. I replaced all the stainless balls in my hand pump and axle pump and have never looked back. The one in my injector clack has alowed my injector to work 100% of the time. The slightest leak here, and the injector will heat up and become useless. Because the injector clack ball really takes abuse from the heat an pressure, I replace it very year and it always works.
One place that I had to keep stainless balls is in my steam operated feed water pump. The balls are, of course, on the clacks on the water side of the pump. The pressure delivered by this little positive displacement pump can be quite high. If these balls are "elastic" in any way, you might force a ball past it's seat! Don't ask me how I know! Also, a little leak with a metal ball here is not a problem in this instance. I have never had a ball stick in the pump, maybe they break free when it starts up, I don't really know. It just works!
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Post by Roger on Sept 19, 2020 7:43:21 GMT
That's more complicated than it needs to be. You only need a groove in the ram to take the 'O' ring, you don't need to contrive a pocket outside. The oil reservoir can be in the main body or in a separate cup like I've done. Agreed. Never use a so-called anti-airlock pin either. Water is incompressible, so what happens when you block its only exit with a pin before the ram finishes each stroke? Gary Hi Gary, If you look at the picture, the ram can only go in so far, and at the most inward position the pin on the end doesn't go in that far. There's no way the pin can block the outlet flow. I'm not sure why some designs have this pin really. Maybe it's so that the maximum suction is created when the pump is dry so that the inlet valve is more likely to lift if it has a tendency to stick. However, if you assume that the inlet valve isn't stuck, there should be plenty of suction to prime the pump even if the gap is large. Obviously, if there's a large free space, the bypass is closed and the boiler is up to pressure, a dry pump won't prime. I can't see that this situation is important to cater for. Personally I think the pin is a solution to an imaginary problem. You need to take this volume into account if you're making an air pump or compressor, but not in a water pump.
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Sept 19, 2020 9:12:34 GMT
Mine are not viton, but nitrile from maccmodels.co.uk There is a thread here on another forum about this subject that might be of interest....see references to seat design & ball sizes etc. Cheers Don
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Post by chris vine on Sept 19, 2020 12:35:35 GMT
I purchased viton balls from the Precision Plastic Ball Company! Chris.
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Post by builder01 on Sept 19, 2020 12:43:37 GMT
Mine are not viton, but nitrile from maccmodels.co.uk There is a thread here on another forum about this subject that might be of interest....see references to seat design & ball sizes etc. Cheers Don Nitrile, or, Buna-N will work okay, but, Viton has a much higher temperature specification.
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Post by Deleted on Sept 19, 2020 13:26:12 GMT
Didn't I read somewhere the Viton is not good for steam? accepted that we aren't necessarily talking a seal for steam here although clacks would need to be. From what I've read EPDM and its associates is the seal that's most suitable for steam. I currently have nitrile for most of my seals and silicon for the piston, neither as good as EPDM from what I can see on the charts and I may revisit my choice at some point in the future.
Pete
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Post by builder01 on Sept 19, 2020 14:36:34 GMT
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Post by Deleted on Sept 19, 2020 15:02:14 GMT
Intersting to note that silicon is not recommended in that chart for steam? As for Viton, from what I have read there are 3 main compounds plus some specials so may not be so straight forward. A quick search on Viton and steam showed this quote: Viton is often used as elastomeric seat in butterfly valves. Viton is know to be restistant to 'difficult' chemical media. However, in many chemical resistance lists the use of Viton is not recommended for hot water applications or steam service.2 Jun 2005 End quote: I'm sure that this has been discussed on this forum before when someone pointed out why not to use Viton for steam applications, it may have been something to do with a toxic gas given off? I had planned on using Viton myself until reading this warning. Alas I only know what I have read on the subject, having no training on such things. Pete
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Post by builder01 on Sept 19, 2020 15:22:42 GMT
If Viton should not be used for steam, I don't understand why the McMaster-Carr says it's okay. At any rate, there should only be cold water in an axle pump or hand pump.
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Post by builder01 on Sept 19, 2020 15:35:42 GMT
I did a little research on Viton, and it is true that the older types of Viton are not recommended for hot water or steam. The newer types have excellent qualities for use with steam. This is probably why McMaster-Carr lists Viton as good for use with steam as they are selling the most recent type of Viton balls.
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Post by Deleted on Sept 19, 2020 15:54:17 GMT
I did a little research on Viton, and it is true that the older types of Viton are not recommended for hot water or steam. The newer types have excellent qualities for use with steam. This is probably why McMaster-Carr lists Viton as good for use with steam as they are selling the most recent type of Viton balls. Yes, from what I've read there are 3 main grades plus specials. A and F plus another between which I can't remember. I recall that A is the most widely available, I don't know which grade is for steam, I would assume not A as being the first letter I'm guessing that came first.
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Sept 19, 2020 16:08:07 GMT
What a fantastic thread. Keep up the good work chaps, I'm hoovering it all up!
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Sept 19, 2020 16:16:27 GMT
When I worked on a certain Class of BR diesel locomotives (in the 1990’s), we were briefed that if a locomotive suffered an engine room fire, we were not to enter the engine room until the area had been made safe. I recall that this was because certain seals in the engine’s air intake system were “Viton”, that if heated above a certain temperature, released Hydrofluoric Acid that was very hazardous to human skin.
I have no other knowledge of Viton these days, maybe this is no longer valid, but it’s something I’ve always remembered....
Cheers Don
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Post by builder01 on Sept 19, 2020 17:31:28 GMT
I would guess that setting any plastic or rubber on fire would release gas that would not be good for you. Other than the coal, do not set your loco on fire!
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stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Sept 19, 2020 17:41:27 GMT
PTFE is notorious for producing hydrofluoric acid when heated above a certain temperature. When I started my career in electronics, we were still using valves, and PTFE valve bases had just come in. I heard of a guy who put his cigarette down, and unbeknown to him, rested it on a PTFE valve holder. When he puffed his cigarette again, it had a most undesirable effect.
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Post by Jim Scott on Sept 19, 2020 19:51:08 GMT
When I worked on a certain Class of BR diesel locomotives (in the 1990’s), we were briefed that if a locomotive suffered an engine room fire, we were not to enter the engine room until the area had been made safe. I recall that this was because certain seals in the engine’s air intake system were “Viton”, that if heated above a certain temperature, released Hydrofluoric Acid that was very hazardous to human skin. I have no other knowledge of Viton these days, maybe this is no longer valid, but it’s something I’ve always remembered.... Cheers Don Hi Don In the past I have used Viton o-rings on experimental laboratory equipment, including vacuum furnaces. The potential risk for Hydrofluoric Acid burns due to overheating in this application was noted but the risk was regarded as relatively small, even though we pushed the temperature rating at times. However, where we really took great care was when HF was used as an etchant in the Metallurgy Lab. Knowing the danger of accidental acid burns and having the appropriate first aid treatment available (Calcium Gluoconate Gel) was essential, but what really stuck in my mind was not to use glass bottles or dishes. HF seriously dissolves glass....! The UK HSE have published info regarding fluorelastomers in relation to car fires which makes interesting reading. Cheers
Jim
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Sept 20, 2020 1:31:51 GMT
Agreed. Never use a so-called anti-airlock pin either. Water is incompressible, so what happens when you block its only exit with a pin before the ram finishes each stroke? Gary Hi Gary, If you look at the picture, the ram can only go in so far, and at the most inward position the pin on the end doesn't go in that far. There's no way the pin can block the outlet flow. I'm not sure why some designs have this pin really. Maybe it's so that the maximum suction is created when the pump is dry so that the inlet valve is more likely to lift if it has a tendency to stick. However, if you assume that the inlet valve isn't stuck, there should be plenty of suction to prime the pump even if the gap is large. Obviously, if there's a large free space, the bypass is closed and the boiler is up to pressure, a dry pump won't prime. I can't see that this situation is important to cater for. Personally I think the pin is a solution to an imaginary problem. You need to take this volume into account if you're making an air pump or compressor, but not in a water pump. Most definitely an imaginary problem Roger! However I think we are at cross-purposes about the pin. In both drawings on the previous page, the 'pin' (so-called) is blocking the exit of the water from the main bore of the pump, and the ram is drawn as filling the cylinder at the end of its stroke. I agree it doesn't protrude into the vertical waterway, but that doesn't matter. As the ram nears the end of its inward stroke, pushing incompressible water in front of it, there comes a point a few mm before the end of the stroke when the outlet hole is suddenly filled with this pin, and a quantity of water is forced to try and squeeze between the pin and the wall of the outlet hole. I think LBSC was the perpetrator of this peculiarly stupid device, which has been 'conventional wisdom' ever since! Gary
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Post by suctionhose on Sept 20, 2020 2:30:20 GMT
The purpose of the 'pin' is to displace as much air as possible out of the pump during the priming stage. With a volume of compressible air inside the pump and boiler pressure working against it, you can have the effect of repeatedly compressing the air bubble without actually displacing anything. Ie the pump won't prime.
I guess you said that in the post above and suggest using the bypass route without backpressure to complete the priming. Still, with a stuck suction and volume of air that is spongey it's a problem. My traction engine suffers from this.
Of course, the pin must have space around it to pass water at the inward extreme. It is just a solid piece to take up air space.
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Post by steamer5 on Sept 20, 2020 13:47:56 GMT
Hi guys, As a thought if the pin is a few thou less in diameter than the hole it goes into then any air that is on the plunger side will be forced out easily, any residual air volume will be very small (depending on how close to the end of the plunger chamber the plunger goes). Next pump cycle will mean the volume of water will be greater & likely force out more or all the remaining air.
Cheers Kerrin
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Post by andyhigham on Sept 20, 2020 15:11:11 GMT
If the pin is only "a few thou" smaller, when the pin enters the hole it could cause a partial hydraulic lock. I wonder if this is the reason some locos with axle pumps can be jerky?
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