Diaphragm fabric

[Harold_V]

All,
I am near being operational with my induction furnace. Considering it's quite old, there are items in its construction that are not necessarily available today, but they are a requirement for its (proper) operation. One of them is a low water pressure cutout switch. It prevents operation of the power supply unless there is adequate water pressure, which cools the entire system.

I have the switch, but have had no luck finding replacement components (the power supply was built in the early '60's). Aside from the diaphragm, it appears to be functional, so I plan to make a new one, plus I'll make the cover from stainless, to prevent rusting, which was a real problem with the original, as the orifice was rusted shut.

So then, my dilemma. I've spent more than two hours scouring the internet, hoping to find a source for the fabric used in making diaphragms, but have not enjoyed success. The original diaphragm measures 2¼" diameter, and has no holes in the center, thus I need material without any holes. Six small holes around the perimeter allow for the screws that hold it in place by the cover. The material is .036" thick, and is some type of rubber material over a fabric. I am quite sure 1 mm thick material would work just fine, and if I must, I may even be able to drop down to 1/32". It makes contact only with hot water, not chemicals or oils. It brings to mind a diaphragm commonly found in automotive fuel pumps, if you've ever worked on one. I am hoping to find a source for this material. I'd like to obtain enough to make more than one, in case I screw it up in the cutting process. Any idea where it can be purchased?

Thanks for anything you can provide in the way of guidance.

H

[liveaboard]

Have a look;
https://www.ebay.co.uk/itm/Nitrile-Nylo ... 0005.m1851

That's a UK seller but they will post to you.
Searching for "nitirile sheet" or "neoprene sheet" returns a few sellers too. Maybe you get one closer to home.

It seems that you can get fiber reinforced if you go over 1.5 or 2mm. That might get too stiff for a diaphragm.

[GlennW]

Assuming that you are referring to a fabric/rubber laminate, I have a sheet of 1/64, but that probably won't fit your needs.

I'm pretty sure I bought it here back in 1985...

https://www.hswhite.com/products/rubber ... -products/

I told them I needed diaphragm material and what I got was just like the diaphragm I needed to replace. Fairly similar to your application actually. It was for a fuel transfer pressure sensor with a 3" diaphragm that shut off the pump when the tank ran dry.

[Russ Hanscom]

Check MSC, I have bought diaphragm material there before. They show 1/16" thick. #31937212

[spro]

Grainger would have it.

[armscor 1]

Hi Harold, possible to swap out the pressure switch, many online with NO NC contacts, easier option I think.

[Harold_V]

Hi Harold, possible to swap out the pressure switch, many online with NO NC contacts, easier option I think.

I've given that some thought, but my final decision was to rebuild, as I have yet to find a switch that is corrosion proof, or priced well beyond what I want to spend. The small change I'm making isn't a big deal, and I don't resent the time I'm spending. After all, at my age, the whole idea is to occupy my time in a favorable way. I also enjoy resurrecting things that are no longer functional.

In regards to corrosion---the water side of the switch was fully packed with rust. The orifice was packed tight, so tight that it couldn't build pressure, although I did find what amounts to a drop of water inside---not much considering the cooling system was operated for at least an hour. The new cover I'm making (it's half finished) will prevent that.

Thanks for your thoughts.

H

[Harold_V]

Have a look;
https://www.ebay.co.uk/itm/Nitrile-Nylo ... 0005.m1851

That's a UK seller but they will post to you.
Searching for "nitirile sheet" or "neoprene sheet" returns a few sellers too. Maybe you get one closer to home.

It seems that you can get fiber reinforced if you go over 1.5 or 2mm. That might get too stiff for a diaphragm.

Indications are that modern diaphragm material is thinner than what was used in the existing switch. Aside from the depth of a sealing flange (which I'd most likely have to alter), I'm not convinced the thinner material wouldn't work just fine, although Russ provided a link that lead me to a source for some 1mm material. My problem is that it doesn't make mention of the product for use as a diaphragm, and makes reference to the material as foam, which may be commonplace for those who know that particular product. I have to make sure that my choice is suited to the purpose so the switch doesn't leak. The mention of foam raises serious concern.

I have found a source for some .018" material, although I have no idea of the cost. It comes from a firm that specializes in diaphragms. Wish I knew if it was thick enough to function properly, but I'm willing to gamble if nothing else presents itself. They're located in the US, which is likely a better situation for me considering I am, too.

Thanks for your thoughts! Much appreciated.

H

[Harold_V]

Glenn, Russ & spro---
Thanks to you gents, too. What I'm beginning to understand is that modern diaphragms are thinner than their predecessors. Most likely due to better materials and better quality control. I suspect that the thin material will end up being my choice. I'll have to make a small change in the sealing flange, but that's no big issue, as it's a part of the cover I'm making. The thinner material won't permit as much compression. I'll halve the amount on the old cover, which would yield an equal ratio for the thinner material.

H

[Russ Hanscom]

The material link I listed was for neoprene, which is good for water, gas, oil and is the most common O ring material. Might be suitable for gasoline and alcohol but I did not research that.

[curtis cutter]

Harold, what is the operating pressure of the switch? I have used low pressure comparator switches as well as switches out of washing machines that control tub water levels.

[Harold_V]

From a copy of the original brochure of the power supply, the normal operating pressure should range between 30 and 60 pounds. I have installed a gauge on mine and find that the pump I'm using provides just at 45 psi, so that's the maximum pressure it should see. If it varies, it would drop a pound or two, depending on the amount of flow, which is adjustable.

This switch does nothing aside from preventing the unit from operating should there be low water pressure. Up to now, I've had it bypassed, so I could start the unit for various inspections. Once it starts producing heat, I wouldn't want it to operate without it. One of the components has a warning that it should not be used with less than 25 psi (a high frequency transformer).

For those who don't know, an induction furnace is capable of creating unlimited heat, and can self destruct easily. Without proper cooling, the furnace proper would die a rapid death, as heating is created by a water cooled copper coil which surrounds the melting chamber, located less than 2" from the molten metal. When casting steel or other similar alloys, temperature of the heat can exceed 3,000° F.

H