Mechanical Seal
Mechanical Seal
(OP)
We have a centrifugal pump in our facility using flush Plan 11. Liquid is taken from the pump discharge and connected through an orifice into the mechanical seal at the top flush connection. The Flush (F) connection location is at 0 degrees while the Drain (D) connection location is at 180 degrees.
But I noticed that there was nothing coming out of the drain piping connected to the mechanical seal bottom.
Could anyone explain to me where the liquid flowing into the mechanical seal is disappearing? Is it expected to flow out through the drain point or is it going back into the pump through the throat bushing?
Any help will be appreciated
But I noticed that there was nothing coming out of the drain piping connected to the mechanical seal bottom.
Could anyone explain to me where the liquid flowing into the mechanical seal is disappearing? Is it expected to flow out through the drain point or is it going back into the pump through the throat bushing?
Any help will be appreciated





RE: Mechanical Seal
Not sure on your actually system or seal but usually with a plan 11 the flush fluid passes through the seal and goes back into the pump through the throat bush.
The drain connections are generally used with a quench connection so if you don't have any quench connections then you are unlikley to get any fluid out the drain.
David
RE: Mechanical Seal
In one of the facilities, liquid is seen draining out of the mechanical seal through the drain connection port. But in another facility, nothing was coming out of the mechanical seal. Both facilities are installed with pumps using Plan 11.
What do this two situations suggest.
RE: Mechanical Seal
are you certain the flush tubing/piping is not filled with debris? new installation or existing?
what is pumpage (fluid being pumped)?
is fluid flashing across orifice? process parameters?
has seal recently failed?
i'm certain the situation is simple to explain.
good luck!
-pmover
RE: Mechanical Seal
RE: Mechanical Seal
Regards checman
RE: Mechanical Seal
RE: Mechanical Seal
JJPellin, if mechanical seals are constructed in line with APIstd682, then the convention is 180deg between the flush and drain ports, I stand to be corrected.
Our pump is a multistage pump (7-stage)and the pumpage is crude oil with sizable content of sand. The pump impeller is in between bearings. There are mechanical seals on both ends.
What I find interesting was that the flush piping was connected from the first stage discharge and then piped to both ends of the mechanical seals.
Questions:
1) Could the flush liquid from the first stage discharge flush effectively the seal on the 7th stage end of the pump?
2) Could pumpage flow from the 7th stage through the throat bush since the pressure at the 7th stage will be greater than the 1st stage discharge pressure?
Your thoughts will be appreciated.
RE: Mechanical Seal
Regards checman
RE: Mechanical Seal
RE: Mechanical Seal
Viscous fluids like crude oil are more difficult than they might seem at first glance. Sure there is great lubricity, but there is also a lot of heat generated at the seal faces due to viscous shear. A crude pump that I'm familiar with operates at ambient, but the seals consistently run 60 F hotter than the process fluid because of this. The viscosity also tends to make the faces run further apart, so leakage is increased and more often than not- visible. Try a steam quench on the atmospheric side of the seal to help heat things up and drop the viscosity of the fluid at the faces. Hard faces are a must due to the solids, of course.
Also note that if there is siginificant wear of the bushings/ balance drum between the seal chamber on the high pressure end of the pump and the impeller, the pressure will increase... so when you replace the seals take a look at the bushings.
RE: Mechanical Seal
JJPellin: We use API682 to complement our inhouse standard. API682 requires 3/4" NPT minimum for the process side and 3/8" NPT for the atmospheric side. Thanks again
RE: Mechanical Seal
As the two ends of the seal chambers are connected together through a blancing line, couldn't there be possibility that the pressure in the seal chamber close to the 1st stage suction be more than the 1st stage discharge pressure. This could justify the need to connect the flush line somewhere in between the stages.
Though our multistage pump has the flush line connected to the 1st stage discharge, what is your experience in this area.
RE: Mechanical Seal