GUARNIZIONE DI TENUTA DELL'ASTA DEL PISTONE
Piston rod packings (short form PRP) are used in double-acting reciprocating compressors to seal the crank-side cylinder. Because the packing rings seal on the reciprocating piston rod, they wear out over a period of time. We therefore deliver the sealing elements as spare parts. STASSKOL range of piston rod packings covers all applications used in piston compressors. We manufacture piston rod packings for dry running operations as well as for lubricated service, both as cooled or non-cooled versions. All our designs can be delivered with additional connections for leakage gas, buffer gas, purge gas and temperature monitoring, all adjusted to the operating conditions.
Piston rod packings consist of several sealing chambers with sealing elements and a mounting flange. The reciprocating piston rod is in the centre of piston rod packing. The sealing elements float freely in the sealing chambers and adjust automatically according to wear. Primary sealing ring can be supplemented by pressure breaker, labyrinth rings, guide bushings, support rings, oil wiper rings and, if necessary, O-rings. In general these sealing rings are described as “set of internal parts”. The packing case incorporates the above mentioned sealing elements in annular chambers. With a mounting flange all held together with tie rods.
MODE OF OPERATION
Due to the working pressure in the compressor cylinder the sealing elements are loaded onto the piston rod and against the chamber surface. By doing so, they seal the cylinder. The loading of the sealing elements is energized automatically by the gas pressure. After reaching the wear limit a leakage gap arises at the inside diameter of the sealing rings which still absorbs the varying gas flow. When all sealing rings are worn to the wear limit, the leakage rises over the standard value.
A lot of factors determine the durability of a piston rod packing: consistence of counter surfaces of sealing elements, composition, quantity and distribution of lubricant, composition of the gas compressed – kind, moisture content, contamination and temperature of gas, material and design of sealing elements. Therefore, it is difficult to predict how fast the sealing elements will wear out. However, when the influencing factors will optimized, the sealing elements work significant longer.
The reliability of a piston rod packing depends significantly on the appropriate assembly of the packing with sealing rings. Back-up rings are required if using non-metallic compounds as a sealing ring material. It’s also possible to incorporate in the packing assembly a pressure breakers, labyrinth rings, guide bushings, oil wiper rings and O-seals depending on the operating conditions. If using multi-sectional sealing rings, they are held together with a circular garter spring.
PISTON ROD TEMPERATURE MEASUREMENT
The patented piston rod measurement makes it possible to detect unacceptable heat on the piston rod and to inform the operator if the operation conditions in the piston rod packing change. The temperature measuring ring is made of a material with good heat conduction, and is moveably installed in the temperature measurement chamber. There is a clearance between the inner diameter of the measuring and the piston rod, so that the heat Transfer from the rod to the measuring ring takes place by means of radiation.
The STASSKOL Piston Rod Temperature Measurement is registered with patent
number 10 2006 015 319.
The sealing surfaces of the piston rod packing must be free of damage, corrosion, grooves and dents: Before mounting of the sealing rings the identification of the individual segments has to be checked. At the cylinder arrangement the oil outlet must be placed vertically at the top of the piston rod packing so that the oil can evenly spread on the piston rod. A mismatch of the sealing chambers must be avoided in every case. At the assembly of piston rod it is vital to ensure, that the piston rod thread is covered by a conical mounting sleeve in order to prevent damage to the internal parts of the piston rod packing. The outside diameter of the mounting sleeve must not in any case exceed the nominal size of the piston rod since otherwise the internal parts of the piston rod packing might be damaged. Following the proper assembly of the piston rod packing the necessary service lines must be attached and if necessary, be lubricated before use.