Replacing a Mechanical Seal on a Pump
Let me re-phrase, attempting to replace a mechanical seal on a pump. I was all jazzed up Saturday night. I had an itch. This itch could only be solved by having more cowbell. Nah, I had an urge to do some work. If you saw that recent post about the relief valve without a piped drain, in one of the pictures you maybe saw a set of blue pumps.
Before you get on me, I have done seals before. This one was stubborn and the pump was critical. It had to go back together unrepaired hence the attempting part.
These pumps are pretty small and their purpose is to return steam condensate back to the DFT for the boilers. The condensate is spent steam that has already done its job – transfer heat of course. These blue condensate pumps are pieces of crap. They were designed poorly and these are old, 2 separate issues. One of the blue pumps, the one on the right hasn’t run in about 3 years. The one on the left started leaking out of the mechanical seal about a month ago.
Saturday I had help at work so I decided we would try and tackle it. First though, what is a mechanical seal? Kind of a mysterious little piece of equipment no?
What is a mechanical seal?
- A mechanical seal is a device that helps join systems or mechanisms together by preventing leakage (e.g. in a plumbing system), containing pressure, or excluding contamination.
Wiki also says that there all these different kinds of mechanical seals but in the building engineering trade when we say it, it means one type. The type with the stationary face, the moving face, a spring, and a hydrostatic seal. That is what mechanical seal means to us.
What I did & lesson learned ha ha
I turned off the electrical. The disconnect for the pumps is right above it. Like I wrote, the pump on the right doesn’t run so it has been off. I turned the switch to the other pump to off (it runs based on tank level,) and then opened the main disconnect.
Should be a pic around here, I used my voltage detector to see if anything was hot.
Then I numbered the wires. There were 4 incoming, 3 to the motor, and then 6 internal to the motor. The 6 didn’t matter because they had already been wired properly for that motor.
The ones that mattered to me were the main line and load voltage wires – which one brought in the current and which one let it flow back. How these wires connected basically “told” the motor what voltage he was and what direction to turn. If I hooked one up wrong it may turn the pump in the backwards direction. I numbered those 6. 3 in, 3 out, and did not label the green (ground) wire. Because by code, green is always ground.
After the wires were disconnected, I removed the flexible conduit from the peckerhead – that blue box where the wires are. By removing this snake like piece, I only had to unbolt the motor from the pump casing. Another pic.
Okay. Electrically safe. Mechanical work time.
Whoever designed this contraption made it not easy to work on.
The pump casing is actually part of the piping. It bolts to the tank and then its discharge is fitted to the pipe.
Hopefully you can see here that the motor was only held down by 6 bolts. It also had a small copper line running from the tank that lubricated the pump shaft that also had to be disconnected on one end so that we could lift the motor out. Conveniently, this line was small and behind the motor. There was about 1″ of room between that and the 200F tank. Thanks friend.
I only jerked my hand out like I don’t know, 50 times?
Unscrewed the line, loosened all the bolts.
Ah, I forgot to mention the lesson learned. Damn this is getting too long. Besides making this electrically safe to work on, we also needed to make it mechanically safe to work on.
Again, this is 1 of 3 sets of condensate pumps. Their purpose is to return already nice and heated up water back to the boilers via the DFT to increase plant efficiency. This water has already been heated up to the steam cycle, it saves us from wasting energy from having to get “new” water up to that point.
So, with us having to isolate this to keep from getting scalded, we were going to be reducing the condensate going back by 1/3. This meant we needed to pay special attention to the DFT level and temperature while doing this – more trips to the boiler plant.
This also meant (lesson learned point) that devices that drained to this specific condensate tank could no longer drain to it because we would have the valves shut.
We have two return condensate headers it looked like that fed the tank. Each condensate header looked like it had about 8 devices piped to it plus 3 low pressure steam hot water heaters as well. Each header to the tank was isolable by closing a main header isolation valve which we did. Then we cracked open the drain line each header also had – totally my idea. Nothing.
We waited a minute to see if anything drained, a little spurt here and there. We got ready to unbolt the motor and stuff. Nothing much coming out of the lines. I opened one drain valve all the way, a little stream came out, cool. Opened the other, still little brown squirts.
We started going on unbolting, undoing them evenly. You never want to fully remove one bolt, or take them out in a circle, or take them all out before jiggling it.
And then pow!
The little brown Squirty McJones drain line blasted open. Apparently, it was clogged. Probably due to never being opened before. In its life. The rust had broken free and we had like an instant steam bath. It wasn’t dangerous as it was low pressure. Startling, very hot, and instantly cloudy though ha ha.
Lessons learned – cycle valves regularly, we should have really cycled this one first, I should not have left either drain valve fully open and started work.
Building Engineer Pro Tip:
- We got most of the pump motor unbolted, leaving 2 bolts partway in for the jiggling. We do this to make sure there isn’t much pressure before we fully remove it. You never want to take them all out before doing this because if you do, and for some reason there is a ton of pressure behind it, you are not fumbling around for bolts trying to get a heavy pump back in place.
By leaving 2 opposing bolts in, in an emergency you have those two started, partway in, and the pump casing, or whatever, cannot come off all the way. The more you know.
We then got the pump out as you can see here.
To get at the mechanical seal we now had to remove the impeller. The beefy monster that moves the fluid right? We got a bearing/impeller puller after taking out the impeller bolt and torqued it off. It actually came off pretty easy.
All that was left was to remove the old mechanical seal, install the new one, and put the motor back in place. We had maybe been at this an hour or two. I love this stuff.
Getting at the old seal proved to be difficult. We couldn’t figure out if we had to remove anything else before taking it off. We messed around with it for a while, trying different things. Maybe a key, set screw, we were missing something.
In the meantime, we went to the parts room to get a new seal. Lo and behold we had like 2.5 random mechanical seals on the shelf.
I do not love this stuff.
Are you kidding me? We had one from the 60’s, another to who knows what, and then .5 because it had pieces taken out to use somewhere else. So it didn’t matter that we couldn’t get at the old seal just yet. We didn’t want it off because we didn’t have one to friggin’ replace it with!
Building Engineer Pro Tip:
- If your building, facility, or home has what you have deemed a “critical” piece of equipment – a generator, a fridge, computer – have a spare part for things that may fail on it handy. Otherwise it’s not that critical.
All we could do now was put this back in. My partner’s shift was ending, I was soon to be alone. We really needed to get this back in and running. We really needed to wrap up this post.
The installation process was the reverse of the removal ha ha. Seriously, it was. Since everything had cooled down a little bit, it was even easier. We had it back up and pumping condensate in less than 30 minutes.
Fun project but frustrating. I didn’t get my itch solved because I didn’t solve a problem. But I did learn quite a bit. I learned how to take these pumps out now. When we do get a seal delivered we’ll be the first to volunteer because we could get it out now in under 30.
Because of that steam coming out of the drain though I thought of another big boy project, stay tuned. See if they’ll even approve that one.
Anything in here catch your fancy? There are some related posts around the site you can check out. There’s one on the Fluke voltalert, or one on the basics of pumps here. Glance at the deals below from Amazon, how do they get such low prices?