Loss of compression
A drop in end-of-compression pressure is a direct measurable indication that the cylinder-piston group has lost its seal. Presented below are 67 industrial test reports in which compression was recorded before and after treatment: per cylinder, with a standard compression gauge, bearing the signatures and seals of the enterprises.
The median gain amounts to 13 %. The upper bound of the range falls on cylinders with the largest initial deviation from nominal: the deeper the wear, the more pronounced the restoration of tightness.
Causes of compression loss
Compression is determined by the tightness of the enclosed volume above the piston. Its loss results from wear of the mating surfaces rather than from a single defect: the end gap of the piston rings, wear of the cylinder bore surface and loss of ring elasticity act in combination.
Mechanics of tightness loss
- Leakage past the ring seal. Wear of the ring working surface and an increased end gap open a path for the working mixture into the crankcase. Part of the charge bypasses the power stroke, and the oil in the crankcase becomes saturated with combustion products.
- Wear of the cylinder bore surface. Ovality and taper of the liner disrupt ring contact around the full circumference. Sealing ceases to be uniform, and the spread of compression between cylinders grows faster than the mean value.
- Cylinder-to-cylinder non-uniformity. The spread of compression between cylinders is more informative than the mean: it shows that wear is progressing unevenly and allows the residual service life to be assessed without disassembling the unit.
Measurement procedure
Compression is measured on a warmed-up unit with the throttle fully open and the fuel supply cut off, cylinder by cylinder, with a standard compression gauge. Values are recorded for each cylinder separately — averaging conceals the very non-uniformity for which the measurement is taken.
The reports presented state the readings before and after treatment for each cylinder, which makes it possible to trace not only the mean gain but also the reduction in the spread between cylinders.
Treated assemblies
Compression was measured on the unit; treatment was applied to the cylinder-piston group: piston rings, cylinder bore surface, mating surfaces.
Equipment types
Test reports
Fifteen test reports with the highest recorded gain out of 65 containing a direct compression measurement. The median across the whole body of data is 13 %, the range from 0,7 to 72,0 %. The full list is given in the catalogue.
| ENTERPRISE | YEAR | CHANGE | PARAMETER MEASURED |
|---|---|---|---|
| SE UkrSTC “Energostal”, pilot plant | 2013 | ↑ 35.4% | compression in cylinder 4, 6.5 → 8.8 kgf/cm² |
| Gaztekhservis LLC | 2005 | ↑ 33% | compression across cylinders, 8.0-9.2 → 10.5-11.5 atm |
| Taxi Moy Gorod LLC | 2018 | ↑ 27-40% | cylinder compression, 10-11 → 14 kgf/cm² |
| PTP Pavlogradpogruztrans | 2012 | ↑ 25-36% | compression of the worn cylinders, controller position 5, 22-24 → 30 kgf/cm² |
| Seid-Transavto LLC | 2003 | ↑ 25-65.3% | compression per cylinder, 4.9-5.4 → 8.1-8.2 on the UAZ and 8-10 → 12-12.5 on the VAZ |
| Imstalkon JSC | 2001 | ↑ 25-46% | compression across the cylinders, 3.0-5.0 → 4.0-7.0 kgf/cm² |
| Zaporizhzhia Iron Ore Plant | 2006 | ↑ 20-33% | compression across cylinders, 15.5-33 → 27-40 kgf/cm² |
| AKAR LLC | 2002 | ↑ 20-33% | compression pressure across cylinders, 27-31 → 35-40 kgf/cm² |
| SE “Ukrvodput” | 2001 | ↑ 19.3-37.2% | cylinder compression, 22.6-24.8 → 29.0-31.0 kgf/cm² |
| Tri K LLC | 2002 | ↑ 16.7-36.2% | compression across the eight cylinders, 22-24 → 26-32 kgf/cm² |
| SPK Murman fishing collective farm | 2003 | ↑ 16.4% | compression across the cylinders, 9-10 → 11-11.5 |
| Troyanovo-3 mine, Maritsa Iztok | 2004 | ↑ 14-33% | cylinder compression, 18-22 → 24-26 atm |
| Tatneft, Almetyevsk UTT-1 | 2001 | ↑ 14-22% | cylinder compression, 17-27.7 → 22-30 kgf/cm² |
| Ukrzaliznytsia, Shevchenko depot | 2003 | ↑ 13-72% | cylinder compression, 25-28 → 27-31 and 18-20 → 31-35 kgf/cm² |
| JSC "Krasnoarm. Khleb" | 2001 | ↑ 13-65% | compression in worn cylinders, 5.5-7.5 → 8.5-9.1 |
All 67 test reports in the catalogue →
Limits of data applicability
- Variability of results. The measurements presented reflect the actual performance on the specific equipment of the enterprises studied. No exact reproduction of the percentage figures on other units is declared, since initial wear, load regimes and lubricant properties are strictly individual.
- Documentary transparency. All figures stated are officially confirmed. A full scanned copy of the original industrial test report is placed under each case described, available for detailed examination and download.
Treatment procedures for these assemblies
Piston compressors · Industrial diesel engines · Gasoline four-stroke engines · All procedures