3 replies to this topic

[Rahimzadeh]

Dears:
Please someone tell me about difference between double mechanical seal and tandem mechanical seal?
best for all of you
M.R.Rahimzadeh

[tarafdar]

Dear Mr. Rahimzadeh,
Please visit wikipedia.org.Go to End face mechanical seals.then go for Tandem & Double seals.

[AZIZ_MN]

Hi mr Rahimzadeh,

Double seals

A double mechanical seal is a combination of two seals mounted back-to-back
with a non-hazardous barrier liquid injected between the two seals at [ * ] to [ * ]
PSIG above the stuffing box (or seal chamber) pressure. The barrier liquid comes
from an external source such as a pressurized reservoir in a closed loop piping
system connected into, and out of, the seal gland.

Double seal arrangement is intended to seal the barrier liquid, not the process
liquid. The arrangement consists of an inner or primary seal installed in backward
position, and an outer or secondary seal installed in normal position. The
backward position of the inner seal prevents the barrier liquid from entering the
pump at normal condition. In the event of an inner seal failure the barrier liquid
enters the pump and prevents the process liquid from leaking into atmosphere. In
the event of outer seal failure, the non-hazardous barrier liquid leaks into
atmosphere while the inner seal contains the process liquid.


Tandem seals

A tandem mechanical seal arrangement is also a combination of two seals but
they are mounted in the normal position, as opposed to the back-to- back position
of a double seal. A barrier liquid is also injected between the two seals from an
external reservoir in a closed loop piping system but it is not pressurized.

The barrier fluid is circulated by the centrifugal force effect of a pumping ring in the
seal. The pressure in the stuffing box is higher than in the barrier chamber so
when the inner seal fails the process liquid enters the barrier chamber and forces
the oil reservoir level to rise. A high oil level switch will trip an alarm and the pump
is shut down. The process liquid is piped out from the of the reservoir into a safe
disposal area.
hope this will help
azzu

Edited by azzu, 05 September 2011 - 06:33 PM.

[Rahimzadeh]

thank you dear azzu
your response cleared me