Repeat Seal Failures

[lewisb13]

Suction pressure is 335PSIG
Disch Pressure is 590PSIG
PT is about 155C

Its got a plan 11 on the inner seals with this little bitty seal cooler on there. Delta T right now is about 5 degrees, basically doing nothing. The outer seal has plan 52 on it. About every 4 months or so the seal fails.

 

[lewisb13]

Here is another angle

 

[lewisb13]

So here are some sample photos. The clear sample is Cumene, which is widely used in the plant as a barrier fluid. The dark sample is what the barrier fluid looks like after a couple weeks of operation. Not sure if the product is attacking the seal faces or what. My inclination is to put a 53A in between the seals with nitrogen bottles. Any other ideas? This pump is pumping a clear mixture if benzene and propane and cumene.

 

[lewisb13]

One more thing. The clear sample is what the pump is pumping. We start with Royal Purple 22 in the seal pot on startup

 

[JJPellin]

You did not provide enough information to get much help from us. But, I love a challenge, so let’s take a stab at it.

None of the seal plans you list should include a seal cooler. The pictures show a Plan 21 rather than Plan 11. You did not provide any details about the seal design, configuration or materials of construction. The pictures show a few deficiencies. The seal pots are too small for this pump. We would require 5 gallon pots. The seal pots are too low. The bottom of the pot should be at least 18 inches above the shaft center-line to provide for good thermo-siphon. The seal coolers are too small for a Plan 21. With a product temperature of more than 300 °F, I would expect those coolers to lime up quickly (depending on your water quality). Even with larger coolers, this is too hot for our water system. We would use an air-fin cooler or convert to a plan 23 to reduce the load on the cooler.

You did not mention where the seal pots are vented to. This is rather high suction pressure. I assume that the seals are a pusher design rather than bellows. You did not describe what you see when you disassemble a failed seal.

If we had this pump in our plant, I would recommend a Plan 53, double pusher seal. I would install five gallon pots with cooling water coils. I would use a similar high temperature synthetic oil to the Royal Purple product that you are using. I would have a Plan 23 on the primary seal. I would review the seal materials of construction for compatibility with my product stream.


Johnny Pellin

 

[lewisb13]

Johnny THANK YOU for your response. You are correct. I didnt realize plan 21 was an 11 with a cooler. I cannot go back an edit my posts to provide more information. Do you know how to do this so that I dont have to keep replying to my own thread? If you had a plan 53 on the secondary seal, how would you pressurize it with those high stuffing box pressures? Just use a 12 pack of nitrogen? I first want to get the configuration down and then we can look at material of contruction of gland and faces, as we will likely have to move to a different seal all together.

 

[JJPellin]

Thank you for pointing out my error. Plan 53 will not work well at such high pressure. I have not had good luck with pressure pistons. I would probably stay with the Plan 52 and correct the other problems I mentioned.

You must reply to your own thread to continue the discussion. That is how it works here.

Johnny Pellin

 

[lewisb13]

Check out the inlet and outlet temps to the seal on both pots. You see how the higher temps are switched? And before you say its piped backwards, take a look at the glands. Weird

 

[JJPellin]

I have seen this sort of flow reversal on tandem seals a few times. In two cases, the seals were designed with an axial flow pumping ring that was rotationally specific. In the first case, someone had gotten the bright idea to standardize both seals to the same stock number without realizing this. In a second case, the OEM repair shop had installed a pumping ring for the wrong rotation. The last case I saw with reverse flow of this type was never resolved. The pumping ring was right and it still flowed backwards. We still need to try and figure this one out. It looks like your seal glands are drilled for tangential ports. This should help to drive the correct flow path. I assume your pump is counter clock-wise, as viewed from the driver. The seal drawing should be reviewed for design. The axial position of the ports could be set-up wrong for one seal.

Johnny Pellin