liquid ring vacuum pump
liquid ring vacuum pump
(OP)
We build vacuum dry kilns for the forest industry. We have been building them for about 20 years. These machines usually run 24/7. We use liquid ring vacuum pumps. We have recently started having trouble with one that was installed about six months ago. Sometimes it trips the VFD. The operator says it won't turn unless you use channel locks. This pump is relatively small at 7.5 HP. The operator says that after it "loosens up", it starts and runs with no problem. In this process, the pump is started and stopped about four times an hour. It will start over and over then it will need the pliers. Does anybody have any idea what is going on? It's not flooding and the coupling is in alignment.





RE: liquid ring vacuum pump
Could it be full of sawdust?
... fouled with wood resin?
What about the seal water? Correct flow? Correct temperature? No particulates?
Mike Halloran
Pembroke Pines, FL, USA
RE: liquid ring vacuum pump
We always use mechanical seals.
We always have strainers in the seal water supply.
We always use condensers before the pump.
We have a flow meter in the seal water supply coming from a cooling tower.
But thanks for your suggestions. And like I said, this kiln has been running about six months but our first kilns from twenty years ago are still running.
Den
RE: liquid ring vacuum pump
Have you thought about changing out this particular unit for another?
Have you have a close inspection of the v/pump,motor and VFD after a stoppage?
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: liquid ring vacuum pump
This pump is relatively small but it's still $5000.
Unfortunately, the installation is several hundred miles away. We are connected through a supervisory computer and input from the operator.
Yesterday the operator had to reset the freq drive repeatedly. Today it cycled on and off all day with no problem. It just doesn't make any sense.
RE: liquid ring vacuum pump
I'd suggest a trip to witness, in person, disassembly and inspection of at least the adjacent piping if not the pump itself.
Mike Halloran
Pembroke Pines, FL, USA
RE: liquid ring vacuum pump
RE: liquid ring vacuum pump
The tank at the end is temporary seal water for testing. Here's another.
The grey shell and tube is the condenser. The condensate falls into the SS tank. Everything has strainers.
RE: liquid ring vacuum pump
Mike Halloran
Pembroke Pines, FL, USA
RE: liquid ring vacuum pump
RE: liquid ring vacuum pump
RE: liquid ring vacuum pump
If the inlet line is becoming blocked or full of water then yes, the vacuum pump won't like it.
For any intermittent fault you just need to look at potential causes and gradually wipe one off after another. Start with easy things like checking all the sensor inputs - impulse lines can block and calibration of instruments can drift. If the control system is getting duff info it will make bad decisions.
The key one will probably be a need to strip down the vacuum pump or at least remove all the connections and have as good a look inside the pump and piping as possible.
A good log of what was happening each day and trip will help as operators have a habit of not telling you the full story and blaming the pump is an easy out. Getting access to the control system historian is a good idea to see what was actually happening as opposed to what should happen.
Let us know what you find, but clearly something is not right on that bit of kit and my feeling is that it is not the vacuum pump....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: liquid ring vacuum pump
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: liquid ring vacuum pump
We are trying to be methodical. I'm trying to stay out of direct contact with the customer and a technician is doing the talking. We don't want to overwhelm the customer. The technician and I have regular meetings.
We used to connect the freq drive to modbuss but they are too noisy. We have asked the customer to give us readings.
We asked the customer yesterday to help us log problems and readings.
Thanks again.
RE: liquid ring vacuum pump
Is that normal?
Why have got a VFD if it starts and stops so much?
what are the complete loss of vacuum - when they load the chamber with more wood?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: liquid ring vacuum pump
When drying wood, we use a chamber pressure set point to set the boiling point of water and therefore the temperature of the wood. Then we operate over a deadband. While pressure is going up, the wood is heating. When pressure is pulled down, evaporation is rapid. On/off is part of the process that has given us phenomenal results over the years.
Now you see why this intermittent problem is so perplexing?
Complete loss would indicate the chamber was opened.
RE: liquid ring vacuum pump
Only other thing I can say looking closely at the photos is whether the condenser piping works well. Looks to me like the air inlet is at the bottom fighting with the condensate drain down to the stainless steel tank and also the line from the top of the condenser doesn't look like it has a slope on it back to the condenser. If you're getting start / stop then is there possibility of water collecting in it over time which then hits the pump as a slug?
Try angling all the inlet pipe back to the condenser as an easy win to eliminate this.
Otherwise there must be something different in this kiln than others. Type of wood? wetness of wood ( is that the correct term?)
relative number of cycles?
intermittent problems are the worst because you are never really sure if you fixed it....
You may just have a badly set up pump which heats up and then jams.
Keep at it and let us know if you discover anything.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: liquid ring vacuum pump
We have dried many species of wood around the world. This customer is drying common North American species. Wetness of wood is called moisture content. Again, nothing out of the ordinary.
Since some of you are interested and have shown an interest, here's a piping diagram.
https://res.cloudinary.com/engineering-com/image/upload/v1466013866/tips/Cooling_Water_Schematic_2_anujko.pdf
RE: liquid ring vacuum pump
It's the sort of thing that, when you personally, in person, arrive, and start inspecting the unit, you will say to yourself, "How the hell did THAT get put on the truck?", probably within a minute of arrival.
Sometimes there is no substitute for being there.
Mike Halloran
Pembroke Pines, FL, USA
RE: liquid ring vacuum pump