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We have a chiller circuit using the Bitzer screw compressor 170. (semi hermetic compact screw). recently it started to fault on "oil Pressure". The sight glass shows a good level of oil, there are no oil leakages, though at time the level seems to drop to nothing. the system is charged with 407a and has no leaks.
Any guys out there who could point me in a direction. My next step will be to check the oil return controls, is there anything else im missing.
thanks
Davezz:rolleyes:
Oil filter clogged?
Davezz.
NoNickName is probably correct. I don't work on Bitzer Screws. But most of the types I do, monitor the oil pressure differential across the oil filter. So if this is the case with the type you have, or not it's still a good place to start. Also when did anyone do any oil related maintenance? IE How Old is the oil, what condition is it in? When was the filter last changed. What are the maintenance intervals reccomended by Bitzer?
All points relevant to your problem.
I hope this post was of some help as it's allways difficult to second guess what is happening.
So for future referance the more detail you can post the easier it is to diagnose the issues.
Cheers Grizzly
WHat is your discharge pressure doing during this time?
Ken
the bitzer screws I have installed have an electronic gizmo in the oil supply line, rumour has it the they tend to play-up intermitently. The oil filters have minimal surface area and need to be replaced at least twelve monthly, with the discharge temps they operate at oil does deteriate and should also be changed annually. here the oil is priced like liquid gold.
regrads Magoo
Hi DaveZZ Magoo is right about the electronic gizzmo, it's a oil flow switch and can get crap on it and cause the oil fault. This will be in the oil supply line to the compressor and looks like a small valve body with conduit going to it. They have a small grub screw that locks the sensor in place and if the position of this sensor has moved it could be causing your problem. if this is a standard Bitzer rack it probably doesn't have an oil cooler and the oil temp will be pretty high. This is the reason you need to change the oil filters and oil annually and it may be a good idea to advise the client to fit an oil cooler. We have done this on several Bitzer racks and it has solved a lot of problems. It can either be refrigerated or air cooler with a 3 way mixing valve fitted to maintain a good oil temp in colder months. Paul
The "gizmo" looks at oil flow and not pressure. probably the filter. Post the outcome so that we know what goes on.
Hi Guys Davezz here, sorry for the delay, work and all. All of you, thanks, you pointed me in the right direction. That "gizmo" an interesting design, yes its an oil level "limiter", a small hollow metal ball rising and lowering, on a hollow tube with sensors inside, sending a signal to control oil level in the sump. (and it was sticky with crap, creating a less responsive (lag) on oil control.
Also i found that on this bitzer screw compact type, the oil filter is in the oil separator itself! You have to unbolt the bell housing and slide it off to get access and unscrew the oil filter (difficult design) After pushing the gas over to the high side and removing oil, the housing unbolted and slid off (heavey though. I also found some really useful exploded drawings of all bitzer equip that i want to share with you. Go to the Bitzer website, click on their Ep@rts, all you need to know...Fantastic, parts numbers and all...makes us look great in front of the customer. (cheers you germans).
Again thanks guys and good luck.
Davezz, I think you missed a point or two there, the bitzer scews don't have an oild sump, the oild is fed in at discharge pressure near the suction end of the rotors, this in turn cools the rotor/discharge gases and forms the seal between rotors. The ball is only moving to prove flow exists.
Also the filter in the oil seperator is normally a coalescing element, used to remove fine oil mist from the discharge gasses. Its not an oil filter in itself.
Saying that I'm used to seeing Bitzers screws in our own packs, not their own make, so maybe they have something new that I've missed ;)
Regards Steve
Davezz.Quote:
Originally Posted by Plank!
If Steve is correct which is a similar system to Halls AND Sabroe. Then you may find very soon the problem will return.
And if it does that a OIL Change may be necessary.
Let us know how you get on.
Cheers Grizzly.