A multistage compression system uses refrigerant and oil. The multistage compression system includes a low-stage compressor that compresses the refrigerant, a high-stage compressor that further compresses the refrigerant compressed by the low-stage compressor, and an oil return pipe that returns the oil discharged by the high-stage compressor or the oil in the high-stage compressor to the low-stage compressor. The low-stage compressor has a rotary compression part that compresses the refrigerant, a motor that drives the compression part, and a container housing the compression part and the motor. The motor is disposed above the compression part. The oil return pipe is connected to a space below the motor inside the container.

A scroll compressor may include a block insertion groove recessed by a predetermined depth into a rear surface of a non-orbiting scroll to accommodate a discharge port and at least one bypass hole, and a retainer block having at least one bypass valve to open and close the at least one bypass hole may be fixedly inserted into the block insertion groove. Accordingly, the at least one bypass valve that suppresses or prevents overcompression in a compression chamber is not fastened to a non-orbiting end plate, which may allow the non-orbiting end plate to be formed thin. As the non-orbiting end plate is reduced in thickness, a length of the at least one bypass hole may be reduced, thereby decreasing a dead volume in the at least one bypass hole.

A method for controlling a compressor system comprising a plurality of compressors, wherein the compressor system is intended to maintain a predefined excess pressure in a pressurized fluid system, wherein decisions are met at fixed or variable intervals as to switching operations for adapting the system to current conditions, wherein—in a pre-selecting step, switching alternatives are excluded from the plurality of combinatorially available switching alternatives, —in a main selecting step, remaining switching alternatives are weighed against one another while referring to one or more optimization criterion (criteria) and optimum switching alternatives are selected from among the given criteria, and—in a control step, the selected switching alternative is output for implementation in the compressor system.

A method for controlling a compressor system comprising a plurality of compressors, wherein the compressor system is intended to maintain a predefined excess pressure in a pressurized fluid system, wherein decisions are met at fixed or variable intervals as to switching operations for adapting the system to current conditions, wherein—in a pre-selecting step, switching alternatives are excluded from the plurality of combinatorially available switching alternatives, —in a main selecting step, remaining switching alternatives are weighed against one another while referring to one or more optimization criterion (criteria) and optimum switching alternatives are selected from among the given criteria, and—in a control step, the selected switching alternative is output for implementation in the compressor system.

Provided is a multi-stage screw compressor with which an intermediate shaft section of a rotor can be made shorter. A two-stage screw compressor includes a front-stage compressing mechanism 1 which has a front-stage male rotor 11A and a front-stage female rotor 11B, and which compresses air, and a rear-stage compressing mechanism 2 which has a rear-stage male rotor 12A and a rear-stage female rotor 12B, and which further compresses the air compressed by the front-stage compressing mechanism 1. The front-stage male rotor 11A and the rear-stage male rotor 12A are configured to be coaxial, and the front-stage female rotor 11B and the rear-stage female rotor 12B are configured to be coaxial. An axial delivery pocket 34 of the front-stage compressing mechanism 1 and an axial intake pocket 39 of the rear-stage compressing mechanism 2 are arranged in a positional relation of partly overlapping with each other in the axial direction of the rotor, and are separated from each other by a separating wall 41.

The invention relates to a method for controlling a rotary screw compressor, having at least a first and a second air-end, wherein both air-ends are driven separately from one another and speed controlled. According to the invention, the following steps are carried out: detection of a volume flow taken at the outlet of the second air-end; adjustment of the rotational speed of both air-ends, when the removed volume flow fluctuates in a range between a maximum value and a minimum value; opening of a pressure-relief valve, if the volume flow falls below the minimum value; and reduction of the rotational speed of at least the first air-end to a predetermined idling speed (V1.sub.L) to reduce the volumetric flow delivered by the first to the second air-end.

The invention relates to a method for controlling a rotary screw compressor, having at least a first and a second air-end, wherein both air-ends are driven separately from one another and speed controlled. According to the invention, the following steps are carried out: detection of a volume flow taken at the outlet of the second air-end; adjustment of the rotational speed of both air-ends, when the removed volume flow fluctuates in a range between a maximum value and a minimum value; opening of a pressure-relief valve, if the volume flow falls below the minimum value; and reduction of the rotational speed of at least the first air-end to a predetermined idling speed (V1.sub.L) to reduce the volumetric flow delivered by the first to the second air-end.

A complete bearing-sealed root vacuum pump system capable of promoting vacuum ability of a condenser of a power plant provides a complete bearing-sealed structure. All chambers are isolated effectively so that liquid cannot flow there between and thus not to destroy the root vacuum pump. Therefore, the lifetime of the root vacuum pump is prolonged. The heat exchangers are arranged between the root vacuum pumps and the front stage pump so as to return the condensed water. The condenser vacuum is improved and thus the power generation efficiency is promoted, and power consumption is lowered. As a result a large power plant can save several thousand tons of coals per year.

Method for operating a pump system preferably comprising more than one pump, comprising the steps of: Obtaining at least one target parameter to be optimized based on target values of each pump; Obtaining an operation target, wherein the operation target is provided by one or more of the pumps operating each with an individual operation parameter; Acquiring a relationship for more than one and preferably all of the pumps between the operation parameter and the target value and determine a target function; Determining a maximum/minimum of the target function and obtaining operation parameter of at least one pump; and Controlling of at least one pump to operate with the obtained operation parameter to optimize the target parameter.

Disclosed are a variable capacity compressor operation mode determination method and device, a variable capacity compressor and an air conditioner. The variable capacity compressor operation mode determination method includes: detecting a current value of a compressor at present as A1 before switching an operation mode of the compressor; detecting the current value of the compressor at present as A2 after switching the operation mode of the compressor and reaching a preset time; comparing A1 and A2, determining that the switching of the operation mode of the compressor is successful when a ratio relationship between A1 and A2 satisfies a preset condition, and determining that switching of the operation mode of the compressor is failed when the ratio relationship between A1 and A2 dissatisfies a preset condition.