Patton Divider Block Systems (Patton) has identified an issue with compressor divider block systems that can cause premature wear to rod packing, piston rods, and piston rings. Differential pressure short stroking (DPSS) is the newly discovered phenomenon where the actual divider block output volume is significantly less than the calculated and designed value when the injection point pressure differentials are greater than 100 psi (6.89 bar).
“It’s been well documented that when the divider block system is injecting into the lubrication points, high differential pressures will cause slap back and piston deformation issues,” said Curtis Roys, founder and CEO at Patton. “What hasn’t been apparent until recently is that noticeable output restriction caused by DPSS can occur with a differential as low as 100 psi, and the full effects of DPSS can occur with a differential as low as 300 psi [20.68 bar], depending on the configuration of pressures. In many instances, the required lubricant can be reduced by as much as 50%.”
“When differential pressures are equalized within 100 psi, the divider block operates efficiently,” said Charlie Hughes, systems specialist at Patton. “When differential pressures exceed 100 psi, the pistons begin to short stroke, significantly reducing the output valve of the divider block. The condition is also compounded by the sequential reduction of oil from each divider block. This ultimately creates tens of thousands of dollars in annual maintenance and compressor downtime. Add the cost of labor, downtime, and parts replacement and the number is staggering. This is affecting all divider block systems, regardless of the divider block or compressor manufacturer. The only way to avoid DPSS and ensure the lubrication points are receiving the calculated amount of oil is to equalize the pressures that are upsetting the hydraulic balance of the divider block assembly.”
The Discovery
The story of how DPSS was discovered begins with a proximity switch.
“I installed a new lube system on a customer’s compressor,” said Hughes. “I happened to place a new proximity switch on the highest-pressure block. We fired up the compressor and everything worked properly, and the panel was seeing pulses from the proximity switch. As I gathered up my tools to head home, the unit went down on lubricator no flow.”
Hughes retraced his steps and reexamined every component. Everything checked out. “We fired up the unit a second time. Everything was operating as it should until the operator loaded the compressor. Again, another no-flow shutdown. Every time the operator would load the compressor, it would shut down for no flow,” said Hughes. “It made no sense whatsoever.”
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This article appears in the June 2022 issue of Gas Compression Magazine. Always free, subscribe today and never miss an issue!
