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Single Vs. Double Mechanical Seals

Single Vs. Double Mechanical Seals

Single Vs. Double Mechanical Seals

When selecting a new pump for a process plant how to decide if you need a single or a double mechanical seal?

Is this seal selection based on the pumping conditions (disch. press, vap. press, ..etc), or is there a definite rules for such selection?

I searched in the API682 and API610, but could not find something clear about this issue.

Thanks in advance for your help,

RE: Single Vs. Double Mechanical Seals

what is the fluid being pumped?

generally, for hazardous fluids, double seals are utilized with a barrier fluid between the two seals to prevent leakage to atmosphere.

good luck!

RE: Single Vs. Double Mechanical Seals

I suggest you contact your local mechanical seal rep. this person will best educate and inform you on how you should go about selecting mech seals.

For fluids that will damage the seal faces (fluid with particles in them) you can use a double seal.

There is allot of info on mech seals but in the end you have to make the call. My advice is to learn about them then the decision is made easy.

good luck!

RE: Single Vs. Double Mechanical Seals

Me3, The general rule of thumb is if it can be safely and dependably sealed with a single seal, use one. Most all seals leak a vapor from the high pressure side to the low pressure side. This is the fluid that lubricates the seal faces and dissipates the heat generated from the associated friction. It should cross the faces as a liquid then vaporize when it hits the atmosphere. Double seals are generally used if the product being sealed does not provide sufficient lubrication for the seal faces or if you need to contain the product or its vapors. They are also used when the seal chamber is under vacuum. Remember that fluid leaks from high pressure side of the seal to the low pressure side to lubricate the seal faces. If the high pressure side is a vapor like our atmosphere when the chamber is under vacuum you would be dry running the seal or running it without liquid between the faces. Most seals are not made to be dry running. The seal flush plan Is just as important as the seal itself. But that is a different subject. Good luck finding a good seal guy to work with. It can be difficult to find one that has good real world  application knowledge and not just the stuff they learn from the company they represent. You can throw a lot of technology at a problem that could have been addressed more economically by covering the basics.  Regards Checman

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