How to measure the gap between the crosshead slider and the slideway?
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2-column symmetric compressor, with the first-stage crosshead bearing surface being a lower sliding shoe and the second stage having an upper sliding shoe. The clearance mentioned in the book is on the non-load-bearing surface or the side with the smaller load-bearing area; measurements show that the clearance of the primary crosshead is normal on that side. But the grade 2 clearance is also on the top, that is, on the bearing surface; there is no clearance between the sliding shoe and the slideway either. What’s going on here? Is it due to the gravity of the crosshead during shutdown? Is it only when it is in operation that the upper crosshead serves as the bearing surface, while the lower crosshead creates a gap with the slide rail?
Well, that's how it is. The direction of the force on the slide is related to the rotation direction of the compressor.
When measuring, a feeler gauge is used.
Do not consider which side bears the load during operation; simply measure the gap at the top of the slide. It’s stopped – how is it possible that there’s still a gap between the skid and the runway? The bearing surface exists because, as the crankshaft rotates and drives the connecting rods, the direction of the force applied to the crosshead changes, resulting in force being exerted on the upper and lower slides. After stopping, they all lay on the slide due to gravity.