How to dimension the seal pot for a double seal in a installation?
How to dimension the seal pot for a double seal in a installation?
(OP)
I want to know the things that I have to take into account to dimension the vessel for installing a barrier fluid in a double cartridge seal.
How to decide the dimension of the vessel pot, fluid to use, lenght of the line, controlers to install (fluid level, temperature,...) ?
Is there some guideline I can follow to make this kind of projects?
Thank you for your help.
How to decide the dimension of the vessel pot, fluid to use, lenght of the line, controlers to install (fluid level, temperature,...) ?
Is there some guideline I can follow to make this kind of projects?
Thank you for your help.





RE: How to dimension the seal pot for a double seal in a installation?
RE: How to dimension the seal pot for a double seal in a installation?
I have studied the API standard 682 and I have seen some considerations about the way of lubricating depending on the way of sealing an other things.
My question is: Imagine that we have already decided to use a double cartridge with chamber pressurized and I have to decide the dimensions of the barrier fluid vessel. I know that the fluid has to be compatible with the work fluid. we can imagine water.
The information I would like to have is how to decide the flow rate, the capacity of the vessel, the pressure to apply (+2bar??), dimensions of the connections, what we can know if we need a cooler or not (may be the work temeparture is not high but when working the fluid in the vessel pot can rise),....
Thanks
RE: How to dimension the seal pot for a double seal in a installation?
RE: How to dimension the seal pot for a double seal in a installation?
Johnny Pellin
RE: How to dimension the seal pot for a double seal in a installation?
I think the cartridge does not have pumping ring. When is it important to have it? What things have you to take into account in the cartridge connections and pipping if the pumping ring does not exist?
Is it better to install an additional cooler then?
Thanks
RE: How to dimension the seal pot for a double seal in a installation?
RE: How to dimension the seal pot for a double seal in a installation?
I attach a drawing of a double cartridge seal back to back without pumping ring (I thing).
If there is not this devive and considering the position of the connections, do you think I could install a 53 lubrication Plan as a thermosiphon system o I should put a forced circulation fluid to improve the flow? And if due to the lack of the pumping ring the flow is not very good and the temperature in the seal pot increases, then to put a cooler?
What recommendations can you give me?
Thanks a lot.
RE: How to dimension the seal pot for a double seal in a installation?
RE: How to dimension the seal pot for a double seal in a installation?
Looking at the seal end view you have supplied - if the shaft is rotating clockwise then the left hand connection needs to be the outlet.
Use a minimum of 1/2" pipe or 3/4" tubing to connect between seal and pot, Mount the pot as close to the seal as you can and at least 18" or 500mm above the seal. Use all up-sloping pipe with the minimum of fittings and large radius bends.
The seal return to the pot is usually in the side and you should not allow the barrier fluid level to drop below the return line - or there is danger of nitrogen entrainment. Also thermosyphon will not work.
There should remain enough space above the liquid at full to at least accommodate thermal expansion. In practice, the upper (and lower) level of liquid is usually determined by a level gauge. The volume that the difference between high and low levels represents has to be compared with expected seal leakage and should be enough for 25 days between successive refills. So, if for example you have 2 litres between high and low level and your expected seal leakage is, say, 3 cc/hr, you will have 2000/3 = 666 hrs = around 28 days between top ups.
The previous posters are correct that by rights, you need to calculate the heat generated by the seal itself, plus any heat conducted from the pump casing and confirm that your seal pot is capable of dissipating that heat load. All seal vendors will have the ability to perform the heat load calculation and can tell you the expected temperatures in the system. As a general rule, with either water or oil-based barrier fluids you don't want this to exceed 80 degC (although may want considerably less on safety grounds - unless you are to put gaurding in place to prevent inadvertent contact with the system. Of course, if you are capable, it is not difficult to perform the heat load calcs yourself. (I've been in the seal industry 20 years, but I couldn't do it!!!)
Instrumentation wise, a Plan 53A vessel should have a level gauge, a low level alarm and pressure gauge and low pressure alarm. Barrier pressure should generally be set at 2 bar above seal chamber pressure.
A trap that many fall into is pressurising the pot with (typically) nitrogen and then shutting the nitrogen supply off - whereas in fact the nitrogen supply should remain on, so that you control only on barrier fluid level and not pressure.
All of the above info is available in API 682, which is a goldmine of information - especially the annexes and appendicies.
Hope this helps a little.
RE: How to dimension the seal pot for a double seal in a installation?
I guess, in an normal situation one can calculate the heat genetation on the faces and once the flush fluid is decided and limiting the maximun temperature rise in the seal chamber (according to 682 standard) you can get the fluid flow. With this information one can now also if it is needed to have a forced circulation or not. Is it like this? All this is a bit confused to me.
For sure you have more experience in this kind of mountings.
RE: How to dimension the seal pot for a double seal in a installation?
What I can say is that, provided the pot is piped up correctly to the seal, you are unlikely to need forced circulation.
Good circulation is indicated by the difference in temperature between the return line to the vessel and the supply line to the seal. Ideally this should not exceed 10 degK, if it does then the circulation is poor.
You might however need additional cooling; either in the shape of a cooling coil within the pot or an external cooler. This is where you need the calculations - to determine whether the heat will be dissipated through the vessel alone or whether additional cooling is required.
It is the latter aspect which determines the overall temperature of the system.
To illustrate the above with some numbers:-
a) If, during normal operation, you had 52 degC on the supply line and 60 degC on the return line (measured, say, half way between the seal and the pot) then this indicates good circulation (8 degK difference)and adequate heat dissipation.
b) 85 degC supply and 90 degC return indicates good circulation but insufficient heat dissipation.
c) 40 degC supply and 60 degC return indicates poor circulation but adequate heat dissipation.
d) 80 degC supply and 120 degC return indicates both poor circulation and inadequate heat dissipation.
Hope this helps you to visualise things a little better. Sorry I can't help with the calculations.