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Howden XRV 127 Compressor

The Howden XRV 127 oil-injected compressor is a volumetric rotary unit filled with oil with controlled power.

Compressors from the XRV range are able to change the liquid coefficient by changing the size of the exhaust channel. This is done by installing a screw to obtain the desired ratio between 2. 6:1 and 5. 0:1. Clockwise for Vi = 2.6, counterclockwise for Vi = 5.0.

Compression is achieved by combining two screw rotors on parallel shafts installed in the crankcase.

Properly machined screw rotors are called “dad” and “mom”. The “dad” (leading) rotor has four cams, which are combined with six grooves in the “mother” (slave) rotor. At the same time, both rotors have the same outer diameter. Each rotor is supported by two cylindrical roller bearings.

The lubrication is carried out in working condition with a differential pressure between the suction and discharge pressures of the compressor. Gaps in the bearing are formed at suction pressure; oil is supplied to the compressor from the oil/gas separator using the discharge pressure exerted on the oil in the separator. When starting, it may be necessary to use an additional oil pump to supply oil to the bearings until the compressor generates sufficient differential pressure to maintain its own oil pressure. This depends on how long it takes to reach the required differential pressure in the system.

The rotor thrust is adjusted by angular contact ball bearings on both types of rotor (“male” and “female”), as well as on discharge drums at both ends of the rotor “dad”. One side of each discharge drum is subjected to lubricating oil pressure and the other side is subjected to suction pressure. Therefore, the discharge drums are located opposite to the normal rotor spacer and as a result, the angular contact bearings receive a light load and last a long time.

The “dad” rotor has blades formed in a spiral along the entire length of the rotor. These blades coincide with the corresponding grooves on the “mother” rotor. Combining and separating blades and grooves inside the compressor crankcases creates additional gaps that increase the volume (suction phase) to a point determined by the shape of the suction channel, where the interblade space is compacted. As the rotors rotate, their blades and grooves reunite, and the gas trapped in the interblade space is compressed. At a point determined by the shape of the exhaust channel, the decreasing interblade space opens for release, and the gas escapes under pressure.

Power control is achieved by means of a spool in the crankcase, controlled by a piston in the hydraulic cylinder that is mounted on the compressor. The movement of the spool changes the point at which gas compression begins, allowing it to recirculate back to the suction phase from the beginning of the compression phase. This reduces the volume of compressed gas. At the same time, the spool changes the size of the exhaust channel to maintain a constant compression ratio. Thus, it is possible to control power from 100% to 10% with approximately proportional energy savings.

The drum is driven by lubricating oil supplied from the lubricating oil manifold to the outside of the drum, acting on the spring force. As oil is supplied to the cylinder, the spool will move under load (towards the exhaust end). When the oil supply stops, the spool is “locked” in its position. To unload the compressor, the oil in the cylinder is released into the oil outlet, and the spool moves without load (towards the exhaust end) under the influence of a combination of spring force and gas pressure.

There are various ways to control the hydraulic cylinder. TOROS is ready to assist in this matter if necessary.