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Natural Gas Engine Driven Chiller Problems Part 2

We have a TECOCHILL 150 ton Natural Gas V8 Truck engine driven screw chiller that has been giving us problems with push rods being damaged. We've had to replace a set of 4 pushrods for one bank twice.

 The cylinder block is made of cast iron and has 8 cylinders arranged in a "V" shape with 4 cylinders in each bank. Five main bearings support the crankshaft, which is retained by bearing caps that are machined with the block for proper alignment and clearances. The cylinders are completely encircled by coolant jackets. The engine rating is 159 bhp at 3300rpm with a 10 degree delta T of 44*F - 54*F chilled water.

 This engine was replaced 3 years ago and we recently replaced the engine oil as well. The Chiller mainly operates during swing season bet. March - May & September - November. The first time we had the push rods damaged we thought we were not giving the chiller enough of a load. Which was not the case. Once the push rods were replaced we started up the chiller at a lower rpm about 1300 rpm and gradually raised the speed. When we approached 2600 rpm the engine started to make a loud clapping sound. The end result was we damaged the second set of push rods in the same bank. The other bank of the engine received no damage to any of its rocker arm assembly. We are puzzled as to what the problem might be. So far we know the screw compressor alignment with to the engine is not a factor. If possible we would appreciate some feedback. <strong>This post was edited by an admin on June 16, 2010 11:23 PM</strong>.

 I really appreciated the feedback I received from this previous post. It seems the problem with bent push rods goes deeper. Our local mechanic thinks the problem might be related to increased back pressure. His reason for this thinking is because previously the engine had a 4" schedule 40 pipe for exhaust and recently we installed a 8" stainless steel pipe from "selkirk metalbestos" due to the 4" pipe corosion issue. The engineers felt the larger diameter pipe would be much easier on the engine. The mechanic felt we should've installed a high temperature fan to help get rid of the exhaust. The TECOCHILL manual stated the back pressure be no more than 26" WC at the highest RPM bet 600*F & 1200*F and 15" WC at the minimum RPM. I would appreciate some further feedback on this issue. Here are the previous measurements taken with the 4" SCH 40 pipe in pdf.  



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