The LDPE process involves an extremely high gas pressure in the range of 200 to 300 MPa (2000 to 3000 bar / 29 to 44 kpsi) being provided by so called Hyper compressors. Many of the old machines are still in operation and kept fit for purpose since they still render good service and maintenance costs are well acceptable versus the investment for a new unit. Legacies have been taken over by others if the original OEM does no longer exist.
The Hyper compressor cylinder performance is very much associated with the special arrangement of the frame, and the operation implies a perfect movement of the plungers to reduce radial loads on the packing internals to a minimum. High accuracy alignment procedures are therefore of the essence to obtain the best life of the packings and the driving gear.
Despite their substantial size and mass the manufacturing tolerances, internal gaps and clearances — particularly for the bearings and crosshead guides — are within the 1/100 mm (0.4 mil) range. As practiced for decades for old Hypers the crosshead shoes are still today scraped by hand to make them perfectly fit into their guide.
On the other hand modern laser technique has proven to be the appropriate equipment to ensure the proper quality for the refurbishment of all parts and pieces. The application of such technique — both in the workshop as well as in the field — increases the accuracy of complicated assemblies and also, since laser measurement is quick, reduces down time tremendously.
Last not least carefully followed check list procedures for condition verification provide the best achievable MTBM (Mean Time between Maintenance).
This paper outlines particular focus points of a Hyper to keep it smoothly running for a long time.
