US20070065302A1

US20070065302A1 - System and method for operating a compressor

Info

Publication number: US20070065302A1
Application number: US11/230,204
Authority: US
Inventors: Michael Schmitz
Original assignee: Individual
Current assignee: General Electric Co
Priority date: 2005-09-19
Filing date: 2005-09-19
Publication date: 2007-03-22
Also published as: JP2009509098A; CA2623174A1; EP1934506A1; WO2007035268A1; CN101305229A

Abstract

A compressor that compresses a fluid during a compression stroke to pressurize the fluid includes an inlet adapted to intake the fluid at an inlet pressure. An inlet valve is coupled to the inlet and adapted to employ a valve closing time during the compression stroke. The compressor further includes an outlet adapted to discharge the fluid subsequent to the compression stroke.

Description

BACKGROUND

The invention relates generally to a reciprocating compressor and, more specifically, to a system and method for controlling a valve closing time of a compressor inlet valve.
A compressor is typically used to boost pressure of a working fluid by receiving power from an electric machine or a turbine, and applying a compressive force to the working fluid. The working fluid may be air, refrigerant, or the like. Compressors are typically classified as positive displacement compressors, dynamic compressors or turbo compressors, depending on the method they employ for compression.
Positive displacement compressors are typically used to boost pressure of the working fluid by reduction in volume, and may be further classified into categories of reciprocating compressors and rotary compressors. Reciprocating compressors typically compress the working fluid via a piston reciprocating inside a cylinder. Rotary compressors typically compress the working fluid via a roller revolving inside a cylinder having an eccentricity.
Large industrial reciprocating compressors are often operated at constant speed. Such compressors may be operated at partial load by controlling opening and closing of compressor inlet valves. By varying the timing of the opening and closing of compressor valves, the mass flow of fluid through the compressor is reduced. Hence, overall performance of the compressor over widely varying speed and load ranges may be improved. Those of ordinary skill in the art will appreciate that the phase angle between a crankshaft and a camshaft may be changed so as to adjust the valve timing events. In this way, it is possible to obtain improved performance for a wider range of engine running characteristics and conditions than when fixed valve timing is employed.
In one example, the compressors use a hydraulic actuation mechanism to control the opening and closing of the inlet valve during partial load conditions. The pressure control of the hydraulic actuation mechanism is controlled via electromagnetic valves. Thereby, mass flow of fluid through the compressor is reduced and the performance of the compressor is enhanced. Such hydraulic actuation mechanisms may employ high pressure pipes and in addition electrical connections to each inlet valve. Moreover, such hydraulic systems do not facilitate flexibility in the controlled opening and closing of inlet valve during partial load conditions.
An improved system and method for controlling valve timing of compressor inlet valves to achieve flexibility in partial load operation of the compressor is desirable.

BRIEF DESCRIPTION

In accordance with one aspect of the present embodiment, a compressor includes an inlet adapted to intake a fluid at an inlet pressure and an inlet valve coupled to the inlet. The inlet valve is adapted to control intake of the fluid at the inlet pressure through the inlet. The compressor further includes a cam adapted to control a valve closing time of the inlet valve during a compression stroke of the compressor to pressurize the fluid. Also included is an outlet adapted to discharge pressurized fluid subsequent to the compression stroke.
In accordance with another aspect of the present embodiment, a compressor includes an inlet adapted to intake a fluid at an inlet pressure and an inlet valve coupled to the inlet. The inlet valve is adapted to control intake of the fluid at the inlet pressure through the inlet. The compressor further includes at least one blocking solenoid adapted to control a valve closing time of the inlet valve during a compression stroke of the compressor, the at least one blocking solenoid being further adapted to maintain the inlet valve at least one stop point during the compression stroke of the compressor.
In accordance with another aspect of the present embodiment, a method of operating a compressor includes supplying a fluid at the inlet pressure via an inlet. The method further includes actuating a cam to control a valve closing time of an inlet valve coupled to the inlet during the compression stroke of the compressor.
In accordance with another aspect of the present embodiment, a method of operating a compressor includes supplying a fluid at an inlet pressure via an inlet; and actuating at least one blocking solenoid to control valve closing time of an inlet valve coupled to the inlet during a compression stroke of the compressor.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
FIG. 1 is a diagrammatical representation of a reciprocating compressor having valve closing control features in accordance with an exemplary aspect of the present embodiment;
FIG. 2 is a detailed diagrammatical representation of a reciprocating compressor having valve closing control features in accordance with an exemplary aspect of the present embodiment;
FIG. 3 is a diagrammatical representation of a reciprocating compressor having a cam adapted to control valve closing time of an inlet valve in accordance with an exemplary aspect of the present embodiment;
FIG. 4 is a graph representing variation of pressure versus volume during a full load cycle operation of a reciprocating compressor in accordance with an exemplary aspect of the present embodiment;
FIG. 5 is a graph representing variation of pressure versus volume during a partial load cycle operation of a reciprocating compressor in accordance with an exemplary aspect of the present embodiment;
FIG. 6 is a diagrammatical representation of a reciprocating compressor having a plurality of blocking solenoids adapted to control valve closing time of an inlet valve in accordance with an exemplary aspect of the present embodiment; and
FIGS. 7 and 8 are flow charts illustrating exemplary processes of operating a compressor in accordance with certain exemplary aspects of the present embodiment.

DETAILED DESCRIPTION

Referring generally to FIG. 1, in accordance with several aspects of the present embodiment, a compressor 10 includes a piston 38 slidably inserted inside a cylinder 42. A suction valve assembly 46 is provided for opening and closing a suction hole 11 mounted at a front side of the piston 38. The suction valve assembly is adapted to control intake of fluid through the suction hole 11. The compressor 10 further includes an electromechanical valve mechanism 52 adapted to control a valve closing time of an inlet valve (not shown) during a compression stroke of the compressor 10 to pressurize the fluid. A control unit 54 may be coupled to the electro-mechanical valve actuation mechanism 52 and configured to control the operation of the valve actuation mechanism 52.
Referring now to FIG. 2, this figure additionally shows further optional exemplary aspects for compressor 10 which are described in greater detail. The reciprocating compressor 10 may be used for domestic and industrial purposes. The compressor 10 is typically driven by an electric motor, steam or gas turbine, combustion engine, or the like. As appreciated by those of ordinary skill in the art, the compressor 10 may be used to compress air, hydrogen, methane, butane, or other liquids or gases. The reciprocating compressor 10 includes a suction pipe or inlet 12 and a discharge pipe or outlet 14 coupled to a casing 16. The suction pipe 12 is configured to receive a fluid at an inlet pressure and the discharge pipe 14 is configured to discharge a compressed fluid. The inlet pressure of the fluid may be ambient pressure or any other appropriate pressure as known to those skilled in the art. A reciprocating motor 18 is disposed inside the casing 16 for generating a reciprocation force. A compressing unit 20 is also located inside the casing 16 and configured to compress the fluid by receiving the reciprocation force generated from the reciprocating motor 18. A plurality of frames 22, 24, and 26 are provided for supporting the reciprocating motor 18 and the compressing unit 20.
The reciprocating motor 18 includes an outer stator 28 having a cylindrical shape and an inner stator 30 disposed along an inner circumferential surface of the outer stator 28. A coil 32 is wound within the outer stator 28. A magnet 34 is reciprocatably disposed in the air gap between the outer stator 28 and the inner stator 30. The magnet 34 is fixed to an outer circumferential surface of a magnet holder 36. The magnet holder 36 is coupled to the piston 38 of the reciprocating compressor 10.
A first resonant spring 39 is disposed between one side surface of the magnet holder 36 and the frame 22 and a second resonant spring 40 is disposed between another side surface of the magnet holder 36 and the frame 24, to induce a resonant movement of the piston 38. The piston 38 is slidably inserted inside the cylinder 42 forming a compression chamber 44. The suction valve assembly 46 is provided for opening and closing a suction hole mounted at a front side of the piston 38. A discharge valve assembly 48 is mounted at a front side of the cylinder 42 for discharging the compressed fluid when a pressure inside the compression chamber 44 is greater than a preset pressure. A fluid suction passage 50 is formed along a longitudinal direction in the piston 38.
When the reciprocating motor 18 is operated, the magnet 34 is linearly reciprocated and thereby the piston 38 coupled to the magnet is linearly reciprocated to compress the fluid. When the piston 38 is retreated, the inlet valve of the suction valve assembly 46 is opened by a differential pressure between the fluid introduced into the suction passage 50 of the piston 38 and the compression chamber 44 of the cylinder 42. When the piston 38 is advanced, the inlet valve is closed and thereby fluid inside the compression chamber 44 is compressed. Also, when a pressure inside the compression chamber 44 is greater than a predetermined pressure, a discharge valve (not shown) of the discharge valve assembly 48 is opened and thereby the compressed fluid is discharged through the discharge pipe 14.
As noted above, during compression stroke, the inlet valve is closed due to differential pressure between the fluid introduced into the suction passage 50 of the piston 38 and the compression chamber 44 of the cylinder 42. In the illustrated embodiment, the electro-mechanical valve actuation mechanism 52 is employed to control the closing of the inlet valve during the compression stroke of the compressor 10 at no-load or partial load operating conditions. In order to achieve flexibility during no-load or partial load operation of the compressor 10, the electro-mechanical valve actuation mechanism 52 enables to control the closing time of the inlet valve during the compression stroke independent of crank motion of the compressor 10. Various exemplary embodiments of the electro-mechanical valve actuation mechanism 52 are explained in greater detail with respect to subsequent figures. The control unit 54 may be coupled to the electro-mechanical valve actuation mechanism 52 and configured to control the operation of the valve actuation mechanism 52. In one embodiment, the control unit 54 includes an electronic logic controller that is programmable by a user. The control unit 54 may control the valve actuation mechanism 52 based on the load condition of the compressor. Those of ordinary skill in the art will appreciate in light of the present discussion that any number of compressor constructions are envisaged.
Referring generally to FIG. 3, one embodiment of the electro-mechanical valve actuation mechanism 52 is illustrated. The electromechanical valve actuation mechanism 52 includes a cam 68 adapted to be electrically driven by a rotary drive unit 70 such as an electrical motor or a rotational solenoid. The cam 68 may be stopped and held in any arbitrary position within the predetermined limits to control the closing of the inlet valve 55 during the compression stroke. FIG. 3 additionally shows further optional exemplary aspects for electromechanical valve actuation mechanism 52 which are described in more detail below.
The inlet valve 55 of the suction valve assembly 46 is provided for opening and closing the suction hole mounted at the front side of the piston. The inlet valve 55 includes a valve plate 56, two plates (58, 60) mutually coupled via a plurality of springs 62. The plurality of springs 62 is provided to bias the plate 58 against the valve plate 56. The valve plate 56 includes a plurality of holes 64 and inlet openings 66. In the illustrated embodiment, the electromechanical valve actuation mechanism 52 includes the cam 68 adapted to be electrically driven by the rotary drive unit 70 such as an electrical motor or a rotational solenoid. The drive unit 70 is operable at constant speed or variable speed. The rotary drive unit 70 may be rotated 90 degrees in an anticlockwise direction to close the inlet valve 55. In certain other embodiments, the rotary drive unit 70 may be rotated 90 degrees in a clockwise direction to close the inlet valve 55. The cam 68 drives a pushing rod (unloader) 72 adapted to follow the motion of the inlet valve 55 and hold the inlet valve 55 at an open position. The pushing rod 72 includes two plate portions (76, 79), a rod portion 74 extending between the plate portions (76, 79), and a plurality of projections 78 extending from the plate portion 76. When the pushing rod 72 is driven by the cam 68, the projections 78 penetrate through the holes 64 formed in the valve plate 56 to disengage the plate 58 from the valve plate 56. Fluid is then sucked through the inlet openings of the valve plate 56.
Although in the illustrated embodiment, one inlet valve 55 is shown, the compressor may include a plurality of inlet valves 55 adapted to control the intake of fluid into the compressor 10. The electro-mechanical valve actuation mechanism 52 may include one cam and one drive unit per valve, in order to operate each valve separately and ensure flexibility. For example, depending on the load condition of the compressor, it may be required to vary the closing time of one set of valves from the closing time of the other set valves during compression stroke of the compressor. The cam 68 is adapted to hold the valve 55 in the open position without the requirement of any external force or energy. The cam 68 may be stopped and held in any arbitrary position within the predetermined limits to control the closing of the inlet valve 55 during the compression stroke.
In the illustrated embodiment, the inlet valve 55 is operable in two modes. During no-load condition or partial load condition, a peak portion 80 of the cam 68 contacts the pushing rod 72 and the inlet valve 55 is fully opened. During full load condition, the cam 68 is disengaged from the pushing rod 72 and the inlet valve 55 is in free floating condition, enabling the inlet valve 55 to be opened and closed due to differential pressure.
In the illustrated embodiment, the control unit 54 may further include a database 82, an algorithm 84, and a data analysis block 86. The database 82 may be configured to store predefined information about the compressor 10. For example, the database 82 may store information relating to crank angle, compressor speed, compressor load, intake fluid pressure, compressed fluid pressure, type of fluid, or the like. The database 82 may also include instruction sets, maps, lookup tables, variables, or the like. Such maps, lookup tables, instruction sets, are operative to correlate characteristics of the valve closing time to specified compressor operation parameters such as compressor speed, crank angle, compressor pressure, compressor load, type of fluid, or the like. Furthermore, the database 82 may be configured to store actual sensed/detected information pertaining to the compressor 10. The algorithm 84 may facilitate the processing of sensed information pertaining to the compressor 10.
The data analysis block 86 may include a variety of circuitry types, such as a microprocessor, a programmable logic controller, a logic module or the like. The data analysis block 86 in combination with the algorithm 84 may be used to perform the various computational operations relating to determination of closing time of the inlet valves 55, predetermined time period for controlling closing time of the inlet valves 55, degree of rotation of the rotary drive unit 70, power required to drive the valve actuation mechanism 52, or a combination thereof. Any of the above mentioned parameters may be selectively and/or dynamically adapted or altered relative to time.
Referring to FIG. 4, a graph representing variation of cylinder pressure versus cylinder volume during a full load cycle operation of the reciprocating compressor is illustrated. Dashed lines 61, 63 represents top dead center position and bottom dead center position respectively of the piston. Operating point 65 represents piston positioned at the top dead center and the discharge valve held in closed position. During intake stroke, the piston is moved to the bottom dead center and is represented by the curve 67. Pressure is reduced and the volume is increased in the cylinder during intake stroke. Operating point 69 represents opening of the inlet valve during intake stroke of the piston and supply of fluid into the cylinder. The inlet valve is opened by a differential pressure between the fluid introduced into the suction passage of the piston and the compression chamber of the cylinder. When the piston reaches the bottom dead center position, the inlet valve is closed as represented by the operating point 71.
During compression stroke, the piston is moved from the bottom dead center to the top dead center and is represented by the curve 73. Fluid inside the cylinder is compressed. Therefore, pressure is increased and the volume is reduced in the cylinder during compression stroke. Operating point 75 represents opening of the discharge valve during compression stroke of the piston and discharge of compressed fluid. When the piston reaches the top dead center position, the discharge valve is closed. The cycle is repeated. In the illustrated embodiment, the inlet valve is in free-floating condition during full load operation. As a result, the compressor delivers 100% mass flow through the cylinder.
Referring to FIG. 5, a graph representing variation of cylinder pressure versus cylinder volume during a partial load cycle operation of the reciprocating compressor is illustrated. As described above, dashed lines 61, 63 represent top dead center position and bottom dead center position respectively of the piston. Operating point 65 represents piston positioned at the top dead center and the discharge valve held in closed position. During intake stroke, the piston is moved to the bottom dead center and is represented by the curve 67. Pressure is reduced and the volume is increased in the cylinder during intake stroke. Operating point 69 represents opening of the inlet valve during intake stroke of the piston and supply of fluid into the cylinder. The inlet valve is maintained in free-floating condition during intake stroke.
When the piston reaches the bottom dead center position, the inlet valve is further maintained in the open position using the electro-mechanical valve actuation mechanism as described previously. During compression stroke, the piston is moved from the bottom dead center to the top dead center and is represented by the curve 73. Fluid inside the cylinder is compressed. Therefore, pressure is increased and the volume is reduced in the cylinder during compression stroke. Since the inlet valve is maintained open for a predetermined period during compression stroke, reverse fluid flow may occur through the inlet of the compressor. Operating point 77 represents closing of the inlet valve during the compressor stroke of the piston. The electro-mechanical valve actuation mechanism is released to close the inlet valve. In the illustrated embodiment, the closing of the inlet valve is delayed using the electro-mechanical valve actuation mechanism. Operating point 75 represents opening of the discharge valve during compression stroke of the piston and discharge of compressed fluid. When the piston reaches the top dead center position, the discharge valve is closed. In the illustrated embodiment, mass flow through the compressor is reduced during partial load condition. For example, during 50% load condition of the compressor, 50% of mass flow is delivered through the compressor. The usage of electro-mechanical mechanism further facilitates to reduce power consumption for maintaining the inlet valve open during compression stroke.
Referring generally to FIG. 6, another embodiment of the electro-mechanical valve actuation mechanism 52 is illustrated. In the illustrated embodiment, the electromechanical valve actuation mechanism 52 includes a plurality of blocking solenoids (88, 90) adapted to be actuated by the control unit 54. The blocking solenoid 88 maintains the inlet valve in an open position for a predetermined time period during compression stroke. FIG. 6 additionally shows further optional exemplary aspects for electromechanical valve actuation mechanism 52 which are described in more detail below.
A drive unit 92, such as a spring or a pusher solenoid, drives the pushing rod (unloader) 72 adapted to follow the motion of the inlet valve 55 and hold the inlet valve 55 at an open position. As discussed above with respect to FIG. 3, when the pushing rod 72 is driven by the drive unit 92, the projections 78 penetrate through the holes 64 formed in the valve plate 56 to disengage the plate 58 from the valve plate 56 and fluid is sucked through the inlet openings of the valve plate 56.
During an intake stroke, the inlet valve is opened due to the differential pressure between the fluid introduced into the suction passage 50 of the piston 38 and the compression chamber 44 of the cylinder 42. In one example, during no-load or partial load condition, the control unit 54 electrically actuates the blocking solenoid 88 adapted to drive a blocking rod 98 so that the blocking rod 98 engages a bore 100 formed in the pushing rod 72. The blocking solenoid 88 is configured to hold the pushing rod 72 at a first stop-point position 102. In this manner, the blocking solenoid 88 maintains the inlet valve in an open position for a predetermined time period during compression stroke. The blocking rod 98 is disengaged from the bore 100 of the pushing rod 72 by releasing the current supplied to the blocking solenoid 88. The pushing rod 72 and the pusher solenoid 92 are actuated in an opposite direction relative to the intake stroke, due to the differential pressure causing the inlet valve to close.
In another example, during no-load or partial load condition, the control unit 54 electrically actuates the blocking solenoid 90 adapted to drive a blocking rod 104 so that the blocking rod 104 engages a bore 106 formed in the pushing rod 72. The blocking solenoid 90 is configured to hold the pushing rod 72 at a second stop-point position 108. In this manner, the blocking solenoid 90 maintains the inlet valve in an open position for a predetermined time period during compression stroke. The blocking rod 104 is disengaged from the bore 106 of the pushing rod 72 by releasing the current supplied to the blocking solenoid 90. The pushing rod 72 and the pusher solenoid 92 are actuated in an opposite directions relative to the intake stroke, due to the differential pressure causing the inlet valve to close. Although in the illustrated embodiment, two blocking solenoids are illustrated, the valve actuation mechanism 52 may include multiple blocking solenoids configured to hold the pushing rod 72 at a plurality of stop points during the compression stroke. One type of blocking solenoid may be used for variety of compressor applications.
FIG. 7 is a flow chart illustrating a method of operating the compressor 10 in accordance with an exemplary embodiment of the present embodiment. The method includes sucking fluid via the suction pipe 12 during intake stroke as represented by step 110. During no-load or partial load operation of the compressor 10, the electromechanical valve actuation mechanism 52 enables to control the closing time of the inlet valve 55 during the compression stroke independent of the crank motion of the compressor 10.
Operation of the rotary drive unit 70 such as the electrical motor or rotational solenoid is controlled via the control unit 54 based on the load condition of the compressor as represented by step 112. The cam 68 is driven by the rotary drive unit 70 as represented by step 114. The cam 68 drives the pushing rod 72 in such a way that the plurality of projections 78 of the pushing rod 72 penetrate through the holes 64 formed in the valve plate 56 as represented by step 116. The fluid is sucked through the inlet openings 66 formed in the valve plate 56. The inlet valve 55 is opened due to differential pressure between the fluid introduced at inlet pressure into the suction passage of the piston 38 and compression chamber 44 of the cylinder 42. The cam 68 is stopped in the predetermined position to control the closing time of the valve 55 during compression stroke of the compressor 10 as represented by step 118. During no-load condition, the peak portion of the cam 68 is engaged with the pushing rod 72 to hold the inlet valve in the fully open position.
During compression stroke, the cam 68 is further actuated by the drive unit 70 to release the cam 68 from the pushing rod 72 such that the inlet valve 55 is closed due to differential pressure acting in an opposite relative to the intake stroke. Thereby fluid inside the compression chamber 44 of the cylinder 42 is compressed. The compressed fluid is discharged via the discharge pipe 14 as represented by step 120.
Referring to FIG. 8, this figure illustrates another embodiment of the method of operating the compressor 10 in accordance with an exemplary embodiment of the present embodiment. The method includes sucking fluid via the suction pipe 12 during intake stroke as represented by step 122. As noted in the previous embodiment, during no-load or partial load operation of the compressor 10, the electromechanical valve actuation mechanism 52 enables to control the closing time of the inlet valve 55 during the compression stroke independent of the crank motion of the compressor.
The drive unit 92 such as the spring or the pusher solenoid drives the pushing rod 72 (unloader) as represented by step 124. The pushing rod 72 follows the motion of the inlet valve 55 and facilitates to hold the inlet valve 55 at an open position. The projections 78 of the pushing rod 72 penetrates through the holes 64 formed in the valve plate 56 to enable suction of fluid through the inlet openings 66 formed in the valve plate 56. During no-load or partial load conditions, the control unit 54 actuates the blocking solenoid as represented by step 126. The blocking solenoid actuates the blocking rod as represented by step 128. The blocking rod engages a bore formed in the pushing rod 72 at a stop point as represented by step 130. The blocking solenoid facilitates to hold the inlet valve 55 at the open position for a predetermined time period during the compression stroke, thereby enabling to control the valve closing time of the inlet valve 55 during the compression stroke as represented by step 132.
As discussed above, during compression stroke, the blocking solenoid is further actuated by the drive unit 92 to release the blocking rod from the pushing rod 72 such that the inlet valve 55 is closed due to differential pressure acting in an opposite relative to the intake stroke. Thereby fluid inside the compression chamber 44 of the cylinder 42 is compressed. The compressed fluid is discharged via the discharge pipe 14 as represented by step 134.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

1. A compressor, comprising:

an inlet adapted to intake a fluid at an inlet pressure;

an inlet valve coupled to the inlet and adapted to control intake of the fluid at the inlet pressure through the inlet;

a cam adapted to control a valve closing time of the inlet valve during a compression stroke of the compressor to pressurize the fluid; and

an outlet adapted to discharge pressurized fluid subsequent to the compression stroke.

2. The compressor of claim 1, further comprising an electric motor adapted to drive the cam.

3. The compressor of claim 1, further comprising a rotational solenoid adapted to drive the cam.

4. The compressor of claim 3, wherein the rotational solenoid is rotated 90 degrees in an anticlockwise direction to hold the inlet valve at a closed position.

5. The compressor of claim 3, wherein the rotational solenoid is rotated 90 degrees in a clockwise direction to hold the inlet valve at a closed position.

6. The compressor of claim 1, further comprising an unloader adapted to be driven by the cam to control the valve closing time of the inlet valve for a predetermined time period during the compression stroke of the compressor.

7. A compressor, comprising:

an inlet adapted to intake a fluid at an inlet pressure;

an inlet valve coupled to the inlet and adapted to control intake of the fluid at the inlet pressure through the inlet; and

at least one blocking solenoid adapted to control a valve closing time of the inlet valve during a compression stroke of the compressor, the at least one blocking solenoid being further adapted to maintain the inlet valve at least one stop point during the compression stroke of the compressor.

8. The compressor of claim 7, further comprising an unloader adapted to be driven by a pusher solenoid.

9. The compressor of claim 8, further comprising at least one blocking rod adapted to hold the unloader at least one stop point during the compression stroke of the compressor.

10. The compressor of claim 9, wherein the blocking rod is actuated by the blocking solenoid.

11. A method of operating a compressor, comprising:

supplying a fluid at an inlet pressure via an inlet; and

actuating a cam to control valve closing time of an inlet valve coupled to the inlet during the compression stroke of the compressor.

12. The method of claim 11, further comprising actuating an electric motor to drive the cam.

13. The method of claim 11, further comprising actuating a rotational solenoid to drive the cam.

14. The method of claim 13, comprising rotating the solenoid 90 degrees along an anticlockwise direction to hold the inlet valve at a closed position.

15. The method of claim 13, comprising rotating the solenoid 90 degrees along a clockwise direction to hold the inlet valve at a closed position.

16. The method of claim 11, further comprising actuating an unloader by driving the cam.

17. A method of operating a compressor, comprising:

supplying a fluid at an inlet pressure via an inlet; and

actuating at least one blocking solenoid to control valve closing time of an inlet valve coupled to the inlet during a compression stroke of the compressor.

18. The method of claim 17, comprising actuating the blocking solenoid to maintain the inlet valve at least one stop point during compression stroke of the compressor.

19. The method of claim 17, comprising actuating an unloader to control valve closing time of the inlet valve.

20. The method of claim 19, further comprising actuating a pusher solenoid to drive the unloader.

21. The method of claim 19, comprising actuating at least one blocking rod via the blocking solenoid to hold the unloader at least one stop point during the compression stroke of the compressor.