Mech Seal Failure

Awad, Welcome. You need to give us some more information. You mention "puffer seal setting" which I guess to mean "Buffer fluid pressure".

If this assumption is correct then we can assume that you have double seals fitted with an API Plan 53. Again if this is correct then your buffer fluid pressure may never be below the maximum pressure that can be experienced in the seal chamber under any circumstances, either static or dynamic.

Please give details of the seal system with barrier fluid pressures (refill pressure and maximum) as well as suction and discharge pressure of the pump etc and we will try to help.

Dear

All your your information correct we use:

Mech Seal Burgmann SHFV (Double,Bulance,face to face and rotating seat)

Pump Centerfugal 4th stage(weir pump)

Buffer fluid pressure 45 bar(Buffer fluid also from Burgmann Auto fill system with Haskel pump and accomulator)

Suction Pressure normal 15 to 10 bar

Discharge pressure 65 bar

In normal operation we not face any problem but this happen at sudden shut down (prime mover is Engine) and trips suction pressure increace above Buffer pressure setting.

Would it be easiest just to fit relief valves on the suction, set at say 30bar?

When the main pump shuts down, relieve the pressure on the seal buffer fluid to a pressure below the suction pressure. That way the seal won't turn itself inside-out:

• Buffer fluid vent valve, with quick-release arrangement fitted?
• Trip the buffer fluid pump?
• Etc.

Dear

At trips actual suction pressure buildup more than 60 bar , and seal buffer fluid 45 bar this cause fail of mech seal

• Buffer fluid vent valve, with quick-release arrangement fitted? Buffer fluid must remain higher than the pressure in the seal chamber at all times. For dangerous products this is deemed to be the shutoff head of the pump plus a safety margin. (Assuming spared service).
• Trip the buffer fluid pump? Would not help as OP says ther there is an accumulator

Awad, How does the seal chamber pressure increase when the pump trips? One assumes that there is a non return valve downstream of the pump, so when the pump trips the seal chamber pressure should revert to suction pressure.

Also, even if the seal chamber pressure increases to above the barrier fluid pressure, the product side seal will not see a very high differential pressure as the barrier fluid pressure remains 45 bar. A very slight contamination of the barrier fluid with pumped product should the only consequence.

The seal should in any case have full reverse pressure capabilities in case your outboard seal fails and you lose your barrier pressure.

Which seal fails - the product side seal or the atmospheric side seal. Also as this is a between bearing pump, do both drive and non drive end seal fail or only one?

What damage are you seeing on the seals? Are the rotating seats positively (mechanicaly) held in place so that they are not dislodged by reverse pressure?

When the pump stops suddenly are you getting excessive axial movement of the shaft?

All good answers, guys. You're right on top of this. Hopefully the OP can understasnd what you said.

Ed Weldon

Dear

There is relief valve in suction setting at 60 bar connect with close tank ,it is easy to change setting bellow buffer fluid pressure 45 bar but we will face problem when station trip (there are four units in station) if all relief valves open i think this crude which returned through relief valve Will effect in close tank

You could, as someone suggested, increase the buffer fluid pressure to, say, 70bar to allow for the suction pressure increase at shutdown. Obviously the problem with this is that, when the pump is actually running the differential pressure between buffer and seal chamber would be more than 50bar; probably not a good idea.

As someone else mentioned, you should expect an increase in suction pressure at shutdown, but from 10-15bar up to 60-65bar? That's quite an increase. I don't know what your system looks like.

If you have relief valves in place on the suction side, you may have no choice but to reduce the setting, since you could argue that they are not doing their job at the moment, and make any modifications to the receiver tanks, etc that may be necessary.