best sealing material for potassium permanganate (KMNO4) at 80 degrees

[t00t]

Is the best material to resist androx at 80 degree PTFE ?

If not what other seals can I use ?

I have a pump that is leaking at the PTFE gasket seal when pumping the androx at 80degree .

 

 

Edited April 7, 2015 by t00t

[DrP]

What is androx exactly? looks like a brand name, what is it chemically? Does this only happen when the temperature gets up to 80C? Is it viscosity related?

 

Has it always leaked at this temperature or has it just started to do this? Maybe the gasket/seal needs reseating/resetting? Strip it down, clean it up and renew the seals.

 

Sorry I can't give you a straight answer - need a bit more info.

[t00t]

Potassium Permanganate . 8% to 10%

 

It happens only after running for roughly 2 hours . Pump and seal is new . Its a new system .

 

We have tried to change the seal . Same thing happen .

 

I don't think it is viscosity because the pump is doing its job . Just that the motor shaft seal is leaking .

 

all interior parts is stainless steel 306 .

 

Could it be the heat is causing a small expansion . Thus causing the leak ?

[DrP]

Well if the pump is new then you could contact the supplier of the pump to explain the problem, maybe they will have some suggestions.

 

If it is as you say and the pump itself is expanding at the seal after a couple hours as it reaches 80C then this could be tested by a) letting the pump cool after a couple of hours before going again, or b) cooling the pump somehow during operation (water or something).

 

Sorry I can't be of more use. Good luck with it. Let us know how you got on.

[t00t]

http://postimg.org/image/mziyt8tub/

The above Picture shows the motor shaft and the PTFE seal.

http://postimg.org/image/kfnbz56ab/

This picture shows after installing the spring that presses the O ring and ptfe tight.

One question though , does stainless steel expand faster then ptfe ?

Oh btw the supplier is half way around the world .

 

 

 

 

[DrP]

You could still e-mail them to find out what the operating temperature of their seals are? Maybe it isn't rated to 80C? If not, then what about a small cooling jacket to keep the seal from expanding.

These charts suggest a factor of 10 difference between the thermal expansion coefficients:

 

http://www.balseal.com/sites/default/files/tr18_020707131421.pdf

 

I do not know if that is relavent or not at 80C. Maybe you can work it out.

[t00t]

Well its suppose to run up to 100 degrees .

At least that's what is says on the catalogue.

Thank anyway DrP

[DrP]

No worries. We have a similar looking seal on one of our pumps. With some of the thicker products it leaks also when we try to filter... we just ignore the problem and wipe the product back in (so professional eh!? ;-) ) - there doesn't seem to be any contamination from the product leaking from the seal, so we ignore it for the volumes we process.

[Enthalpy]

I expect Ptfe to resist permanganate chemically. But I distrust the mechanical and gliding properties of Ptfe: it creeps horribly, it rubs a lot when hot or just lukewarm (the coefficient of friction jumps to 0.3, as bad as any polymer, over something like +40°C already) and then the parts destroy in a runaway worsened further by Ptfe's expansion that grips the shaft. It expands like a bad thermoplastic, like 300ppm/K instead of 17 for stainless steel.

 

Because of that, which is known from manufacturers of seals and gliding parts, pure Ptfe isn't generally used alone as a seal, less so as a mobile seal - not even as a gliding material. It impregnates some mechanically sound material like bronze or polyamide, and if sometimes used at a (static!) seal, then it's strongly helped by additional parts of sound materials.

 

So it looks like Ptfe is just a bad choice to rub, and the chemical isn't necessarily the cause.

 

Making bearing bushes and seal rings are two specialized professions. It's a true knowledge, not common to mechanical designers, and not even published; tinkering that takes months with no guarantee of success. I suggest that you contact a manufacturer and ask him to solve the case.

Edited April 8, 2015 by Enthalpy

[t00t]

I only wish my boss accept the leak . But its gonna be impossible . Beacause of the cost of the chemical . Leaking chemical means lost of money

 

Anyway thanks drp.

 

Thank you enthalpy . Guess I will just have to find a sealing company and make one .