Vilter Recip Compression Ratios

[mr.ice]

We've had a single stage plant running for some years now, consisting of 4 x Vilter 440 series machines, 16, 12, and 2 x 8-cylinder models, on synthetic oil, and NH3.
Head Pressures sit between 7.5 bar (108 psi) and 8 bar (116 psi) and suction of 0.2 bar (2.9 psi).
Years ago this plant ran at 10.5 bar (152 psi) Head Pressure and 0.5 bar (7psi) suction. It was stressing so we lowered the condensing condition which reduced the Head Pressures and it all settled down. Oil temperature sits around 35 - 40 deg Celsius (95F - 104F).
We have received criticism over the compression ratio. We would welcome anybody's opinions and comments.

[sterl]

That's over 7:1 and nearing the 8.5:1 Vilter considers limit on Ammonia And if you can hold those discharge pressures all year around, I don't see it as much of an issue. That geometry of vilter is a tough machine and pretty tolerant of conditions that cause other compressors to wince. Are you running at less than 1200 RPM and do you have a Discharge Temperatire reading?

Had an old 450 on mineral oil; founf out after a while we were better off letting the oil warm up a little but running the heads a little cooler: kept refrigerant and water out of the oil; still gave good oil separation. We piped cold water through the head covers in parallel instead of in series...

[mr.ice]

Hi there Sterl. Thanks for your effort on my behalf. A second opinion is just what I was looking for. You mentioned that Vilter has specified 8.5:1. Can you please point me to where I can find the information about this? I have looked through all the Vilter literature that I have, but have never come across this information.

You asked about rpm. Yes, we are running at 950 rpm. I don't have the discharge temperature in my mind but I am sure that it is nothing unduly high.

[mr.ice]

We have checked again and discharge temp is 105 degrees Celsius. (221 deg F).

Any luck in finding the Vilter documentation or a link to it regarding the recommended ratios? Would appreciate any pointers about tracking it down.
Thanks again for your time.

[US Iceman]

The 8:1 compression ratio limit is legitimate for ammonia. It is not a hard and fast rule, but rather a general recommendation that should not be exceeded. There are some variations of this though. If the RPM is below 1000 for example. These were used as general rules of thumb at Vilter. The limit is due to an attempt to keep the discharge temperature under 300°F in the cylinders.

I believe this is listed in the recip. compressor rating sheets in the operating envelope figure.

[RANGER1]

Due to the constantly low SCT you are getting away with discharge temp .
A normal system would have problems with a design +35 deg C SCT .

[sterl]

I have not looked through all my stuff for the Vilter 440 but the XL machines have (largely) the same operating envelope defined per:

http://www.vilter.com/LinkClick.aspx...id=155&mid=562

See P. 3 and the little banner on top...Says 8:1.

I have seen both Grasso and Sabroe use higher numbers with their recips....In fact a presentation by Mr. Tony Noyes to the IIAR indicates 10:1 for Grasso recips on R-717; through their max discharge temperature tends to shave the top off that at pretty high suction pressures.

[US Iceman]

Thos evalues for compression ratio are the same ones used for eith the 440 or 450, or 450 XL compressors. The maximum differential pressures are different for each series though!