Abstract:
A gas supply system for a mechanical seal turns on the gas supply at a pressurized flow rate at the time of compressor case pressurization and remains on during compressor rotation until pressure is adequate. The gas supply system has an intensifier that includes a pair of mechanically inter-connected pneumatic pressure cylinders which comprise a drive cylinder that affects movement of a boost cylinder wherein the displacement of these mechanically interconnected pistons in the drive cylinder and boost cylinder intensifies the pressure being discharged by the boost cylinder and supplied as a barrier fluid to the mechanical seal. The intensifier uses a control valve and operating system which includes a fast-acting 5/2-way solenoid valve having a feedback loop connected to a control system which includes a micro-processor that controls valve actuation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application asserts priority from provisional application 61/660,931, filed on Jun. 18, 2013, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to mechanical seal system having a fluid intensifier for a dry gas seal system which supplies gas to a mechanical seal and more particularly, to a gas seal system having an improved intensifier which supplies barrier fluid to the mechanical seal. 
       BACKGROUND OF THE INVENTION 
       [0003]    In conventional mechanical seal configurations, various types of rotating equipment, such as pumps and compressors, are provided with mechanical seals to prevent or impede leakage of process fluid that might otherwise migrate along the shaft of the rotating equipment. In many of these mechanical seals, a dry gas serves as a barrier fluid or buffer fluid next to a pair of relatively rotatable mechanical seal rings, which fluid serves to greatly minimize, if not eliminate leakage along the shaft. Such mechanical seals include a barrier fluid chamber for receiving the dry gas therein from a gas supply system. This gas supply system supplies the gas to the mechanical seal at a particular pressure and flow rate which maintains an adequate supply within the fluid chamber of the seal. 
         [0004]    During normal conditions, leakage of process fluid past the seal faces into the barrier fluid chamber is prevented by the higher pressure of the barrier fluid both statically when the shaft is not rotating and dynamically during shaft rotation. Under such normal conditions, small amounts of barrier fluid may flow across the seal faces into the process fluid, although this barrier fluid is of a type of fluid which is not a contaminant if present in the process fluid. However, if inadequate barrier fluid pressure is present, a reverse flow of process fluid may occur where the process fluid undesirably leaks into the barrier fluid chamber. For example, in a compressor, there may be a period when the compressor is being started or is being shutdown, and during these periods, there may not be adequate barrier fluid pressure and flow to prevent a reverse flow of process fluid leaking into the barrier fluid chamber. 
         [0005]    It is an object of the invention to maintain an adequate flow rate of the barrier fluid, even at low-feed operating conditions of the rotating equipment or at start up of such equipment. 
         [0006]    The invention relates to an improved gas supply system which, in particular, relates to an improvement in a gas supply system sold by the assignee of the present application under the trademark AMPLIFLOW™. In the known AMPLIFLOW system, the seal supply system turns on the gas supply at a pressurized flow rate at the time of, for example, compressor case pressurization wherein the seal supply system remains on during compressor rotation. At the point in time when pressure is adequate, the AMPLIFLOW system can be turned off while the compressor system continues running During unit shutdown of the compressor system, the AMPLIFLOW system may be turned on again as compressor rotation comes to a stop and after rotation is completed, then the AMPLIFLOW system can be turned off again. 
         [0007]    More particularly as to the present invention, the invention relates to an improved supply system having an intensifier comprising a pair of mechanically inter-connected pneumatic pressure cylinders which comprise a drive cylinder that affects movement of a boost cylinder wherein the displacement of these mechanically interconnected pistons in the drive cylinder and boost cylinder intensifies the pressure being discharged by the boost cylinder and supplied as a barrier fluid to the mechanical seal. 
         [0008]    While a pneumatic four-way valve has been used in the known AMPLIFLOW system to control the operation of the drive cylinder, this pneumatic four-way valve, as shown in  FIGS. 3-5  of the present application suffers from disadvantages associated therewith as discussed in more detail herein. 
         [0009]    The invention relates to an improved intensifier using an improved control valve and operating system therefore which provides advantages over the prior art. In this regard, the invention relates to an intensifier using a fast-acting 5/2-way solenoid valve having a feed back loop connected to a control system which includes a micro processor that controls valve actuation. As discussed herein, this system provides for remote operation and monitoring and improves the overall performance of the fluid control system. 
         [0010]    Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagrammatic view illustrating a dual-piston intensifier of a gas-supply system of the invention in a first operative condition. 
           [0012]      FIG. 2  illustrates a second operative condition of the intensifier of the invention. 
           [0013]      FIG. 3  illustrates a drive cylinder being driving by a pneumatic four-way valve in a first operative condition of a known system. 
           [0014]      FIG. 4  illustrates a second operative condition of the drive cylinder of  FIG. 3 . 
           [0015]      FIG. 5  illustrates a next operative condition of the drive cylinder of  FIG. 4 . 
           [0016]      FIG. 6  illustrates an intensifier of the invention. 
           [0017]      FIG. 7  diagrammatically illustrates the intensifier and the control system thereof. 
           [0018]      FIG. 8  is an enlarged view of the drive cylinder of the invention. 
       
    
    
       [0019]    Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import. 
       DETAILED DESCRIPTION 
       [0020]    Referring to  FIGS. 1 and 2 , an intensifier  10  of the invention is shown without the control system therefore. The intensifier  10  is a system of pressurized pneumatic cylinders which are operatively connected together to boost or increase the pressure of the barrier fluid gas being discharged from the intensifier  10  and being supplied to the barrier fluid chamber of a mechanical seal. 
         [0021]    More particularly, the intensifier  10  includes a drive cylinder  12  which is operatively connected to a boost cylinder  14  by an intermediate piston rod  15 . The drive cylinder  12  has a pressurized cylinder housing  16  which defines a pressure chamber  17  that is subdivided into variable-volume cylinder chambers  17 A and  17 B by a reciprocating piston  18 . The cylinder housing  16  includes end walls  19  and  20  wherein the piston rod  15  slidably passes through the end wall  20  and through a spacer-like distance piece  21  for connection to the boost cylinder  14 . 
         [0022]    As described in further detail below, the chambers  17 A and  17 B of the drive cylinder  12  are alternately pressurized and depressurized by an air source to drive the piston  18  in opposite leftward and rightward directions and effect a corresponding driving of the boost cylinder  14 . Generally, an air vent  22  is provided to release air leaking from chamber  17 B during rightward movement of the piston  18  which may occur as the chamber  17 A is pressurized by the air source and the piston  18  is driven rightwardly. 
         [0023]    As seen in  FIG. 1 , the boost cylinder  14  has a pressurized cylinder housing  25  which defines a pressure chamber  26  that is subdivided into variable-volume cylinder chambers  26 A and  26 B by a reciprocating piston  27 . The cylinder housing  25  includes end walls  28  and  29  wherein the piston rod  15  slidably passes through the end wall  28  from the distance piece  21  so as to be driven by the drive cylinder  12  described above. 
         [0024]    As the chambers  17 A and  17 B of the drive cylinder  12  are alternately pressurized and depressurized by the air source, the drive piston  18  reciprocates in opposite leftward and rightward directions and affects a corresponding leftward and rightward driving of the boost cylinder  14 . Generally, a gas vent  30  is provided to release barrier gas pressure leaking from chamber  26 A during leftward movement of the piston  27  which occurs as the piston  27  moves leftwardly. 
         [0025]    With this arrangement, the drive cylinder  12  is linked mechanically to the boost cylinder  14 . The diametric area of each piston  18  and  27  differs wherein the area of the piston  18  is larger than the area of the piston  27 . As such, the air pressure driving the drive cylinder  12  boosts or increases the pressure generated in the boost cylinder  14  and being output therefrom for supplying the mechanical seal with barrier fluid. 
         [0026]    To control the discharge of barrier fluid being discharged from the boost cylinder  14 , a valve system  32  is provided to ensure a continuous, pressurized flow of barrier gas during the reciprocating movement of the drive cylinder  12 . The valve system  32  includes a gas inlet  33  that receives a dry gas as the barrier fluid from a gas supply. The gas inlet  33  includes supply lines that split and feed a normally-open first check valve  34  and a normally-closed second check valve  35 . The normally-open first check valve  34  and the normally-closed second check valve  35  respectively connect to a first supply line  36 A that is connected to the cylinder chamber  26 A and connect to a second supply line  36 B that is connected to the cylinder chamber  26 B. The supply lines  36 A and  36 B alternatively can be referenced as inlet lines for supplying the barrier fluid alternatingly to the chambers  36 A and  36 B during operation of the intensifier or as discharge lines when discharging fluid from the chambers  36 A and  36 B. 
         [0027]    The valve system  32  also includes a gas outlet or discharge  39  that discharges the dry gas as the barrier fluid to the barrier fluid chamber of the mechanical seal. The gas discharge  39  includes discharge lines that split and receive buffer fluid from a normally-closed third check valve  40  and a normally-open fourth check valve  41 . The normally-closed third check valve  40  and the normally-open fourth check valve  41  respectively connect to the first supply line  36 A that is connected to the cylinder chamber  26 A and connect to a third supply line  36 C that is connected to the cylinder chamber  26 B. 
         [0028]    The various check valves  34 ,  35 ,  40  and  41  are automatically switchable between open and closed conditions depending upon whether the supply lines  36 A,  36 B or  36 C are subjected to gas pressure during reciprocating movement of the boost piston  27 . 
         [0029]    For example,  FIG. 1  shows a first operative condition wherein the boost cylinder  14  is pressurized by the drive cylinder  12  in the rightward direction, and wherein the drive piston  18  is moved rightwardly by air pressurization of the chamber  17 A which drives the piston  18  rightwardly. This drives the boost piston  27  rightwardly and pressurizes or compresses the gas in the chamber  26 B. In this condition, fourth valve  41  is open to allow compressed gas to be discharged through supply line  36 C and gas discharge  39 , while the incoming supply line  36 B is blocked by closed check valve  35 . At the same time, first check valve  34  is open and third check valve  40  is closed which allows the inlet gas to refill the expanding cylinder chamber  26 A. Hence, during rightward movement of the piston  27 , gas is compressed and discharged from the discharge port  39  to the mechanical seal. 
         [0030]    In the second operative condition of  FIG. 2 , the boost cylinder  14  is pressurized by the drive cylinder  12  in the leftward direction, wherein the drive piston  18  is moved leftwardly by air pressurization of the chamber  17 B which drives the piston  18  leftwardly. This drives the boost piston  27  leftwardly and pressurizes or compresses the gas in the chamber  26 A. In this condition, third valve  40  is open to allow compressed gas to be discharged through supply line  36 A and gas discharge  39 , while incoming gas to this supply line  36 A is blocked by closed check valve  34 . At the same time, second check valve  35  is open and fourth check valve  41  is closed which allows the inlet gas to refill the expanding cylinder chamber  26 B. Hence, during leftward movement of the boost piston  27 , gas is compressed in chamber  26 A and discharged from the discharge port  39  to the mechanical seal. Since one of the chambers  26 A and  26 B is being pressurized at any time depending upon the direction of movement of the boost piston  27 , the gas is continuously discharged from the gas discharge  39  so that a continuous, pressurized supply of barrier gas is supplied to the mechanical seal. 
         [0031]    Turning to the known system shown in  FIGS. 3-5 , this system uses a pneumatic 4-way valve unit  50  to control reciprocating operation of the drive cylinder  12 - 1  wherein similar system components are referenced relative to  FIGS. 3-5  with common reference numerals denoted by the suffix “-1”. Therefore, the drive cylinder  12 - 1  includes the drive piston  18 - 1  which drives a piston rod  15 - 1  to in turn drive a boost cylinder (not shown). The drive cylinder  12 - 1  includes chambers  17 A- 1  and  17 B- 1  which are alternatingly pressurized to reciprocate the piston  18 - 1 . 
         [0032]    Generally, a known drive cylinder  12 - 1  is driven by the 4-way valve unit  50  which includes a drive air supply  51  and a drive air exhaust  52  that are respectively connected to a 4-way valve  53  in a valve manifold  54  by an inlet line  55  and a discharge line  56 . The inlet line  54  has a single connection to the valve  53  while the discharge line  55  splits into two outlet ports  57  and  58  that separately connect to the valve  53 . The valve  53  is also connected to a first supply line  36 A- 1  and second supply line  36 B- 1  which respectively connect to the cylinder chambers  17 A- 1  and  17 A- 2 . In the first operative position of the valve  53  shown in  FIG. 3 , the inlet line  57  is operatively connected to the supply line  36 B- 1  which pressurizes chamber  17 B- 1  and drives the piston  18 - 1  leftwardly. The other chamber  17 A- 1  is vented by the connection of supply line  36 A- 1  to the discharge line  56  through the valve port  57  and the valve  53 . 
         [0033]    To control the operation of the valve  53 , the opposite ends of the valve  53  are connected to first and second control lines  60  and  61  which are alternately pressurizable to move the reciprocating valve member  62  leftward and rightward between the two positions seen in  FIGS. 3 and 5 . The control lines  60  and  61  connect to pilot valve A  63 A and pilot valve B  63 B which in turn connect to the air supply  57  by supply lines  64  and  65 . The pilot valves  63 A and  63 B are switched between open and closed positions upon physical contact with the piston  18 - 1  and spring-biased pilot valve members  66  and  67 . Each of the pilot valves  63 A and  63 B vent through breather vents  64 A and  64 B, which occurs when the piston  18 - 1  separates from the valve members  66  and  67  as seen in  FIG. 3 . This condition allows the reciprocating valve body  62  of the 4-way valve to remain in one end position or the other as seen in  FIG. 3 . 
         [0034]    During cylinder operation, the drive piston  18 - 1  continues moving leftward as seen in  FIG. 3  until its stroke bottoms out against the cylinder end wall as seen in  FIG. 4 . The drive piston  18 - 1  then actuates the pilot valve  63 A by contacting the drive member  66  which opens the pilot valve  63 A and allows intake air to pass from line  64  to supply line  60  which then pressurizes the left side of 4-way valve  53  to move the drive member  62  rightwardly ( FIG. 4 ). This closes discharge port  57  and connects the air inlet line  55  with the supply line  36 A- 1  to start movement of the drive piston  18 - 1  rightwardly. The discharge line  56  connects to the other supply  36 B- 1  by opening of the valve port  58 . 
         [0035]    As the piston  18 - 1  leaves the left end stroke position of  FIG. 3 , the piston  18 - 1  separates from the pilot valve member  66  as seen in  FIG. 5  which closes the pilot valve  63 A but opens the breather vent  64 A to release the air from supply line  60 . This occurs after the 4-way valve member  62  has moved to its rightward position of  FIGS. 4 and 5 .  FIG. 5  illustrates the fluid paths as the piston  18 - 1  moves toward its rightmost stroke position, wherein the piston  18 - 1  would contact the pilot valve body  67  to again switch the 4-way valve  53  and move its valve member  62  back to the leftmost position of  FIG. 3 . Essentially, the pilot valve  63 B would then operate in the same manner as the pilot valve  63 A described above. The 4-way valve  53  and the pilot valves  63 A and  63 B then repeat this operation to reciprocate the piston  18 - 1  in opposite leftward and rightward directions to then operate a boost cylinder. 
         [0036]    This known configuration of  FIGS. 3-5 , however, can encounter operational difficulties. In one error condition, the 4-way valve  53  may stall, for example, when a pump or compressor is not used for extended periods and there may be insufficient lubrication for the 4-way valve member  62  which causes hang up or a resistance to movement thereof. Also, it is possible that the pilot valves  63 A and  63 B may not operate properly which could be related to manufacturing and assembly-related deficiencies or if the valve springs are not in conformance to specifications. 
         [0037]    Referring to  FIGS. 6-8 , an improved intensifier  10  is disclosed which includes the cylinder arrangement of  FIGS. 1 and 2 . Referring to  FIGS. 6 and 7 , this intensifier  10  includes the drive cylinder  12  and the boost cylinder  14  which have pistons  18  and  27  reciprocating within their respective cylinder housings  16  and  25  and which are connected together as described above by the piston rod  15 . 
         [0038]    Flow of a dry gas through the boost cylinder  14  is controlled by the valve system  32 . Hence, the boost piston  27  varies the volumes of the cylinder chambers  26 A and  26 B as the piston  27  is driven by the drive cylinder  12 . To operate the drive cylinder  12 , a 5/2 way control valve unit  72  is mounted to drive cylinder  12  and is operated by a controller  73  ( FIG. 7 ). Preferably, the controller  73  is a computer-based microprocessor such as a PLC which allows the operation of the intensifier  10  to be programmed and selectively controlled and monitored. 
         [0039]    As to the control valve  72 , the control valve  72  preferably is a high speed, fast-acting solenoid valve which has a low power requirement and is suitable for non-lubricated dry air applications. Preferably, the control valve  72  is a 5/2 way valve essentially having five ports or connections. In this regard, the valve includes connection  81  which connects to the source of pressurized air for the drive cylinder  12 . The valve  72  also has outlet connections or ports  82  and  84  which respectively connect to supply lines that in turn are connected to the cylinder chambers  17 A and  17 B. 
         [0040]    Also, the control valve  72  includes exhaust ports  83  and  85  which alternatingly exhaust pressurized air from the control valve  72  and the cylinder chambers  17 A and  17 B during operation of the drive cylinder  12 .  FIGS. 7 and 8  diagrammatically represent the valve structure, wherein  FIG. 8  shows a solenoid control  87  which is selectively operated to move a valve spool  88  between two operative positions. The control valve  72  has a return spring  89  wherein the solenoid  88  is actuated to drive the valve spool  88  from an initial first operative position to the right to a second operative position. When the solenoid is deactivated by the controller  73 , the spring  89  biases the valve spool  88  to the left to the original first position, so that the valve  72  switches between the first and second operative positions to cycle or reciprocate the drive piston  18  leftwardly and rightwardly as described above. 
         [0041]    As seen in  FIG. 8 , the control valve  73  is configured to define multiple flow paths diagrammatically shown in  FIG. 8 . When the spool  88  is in one operative position, a flow path  91  is connected between the intake  81  and the outlet port  84  which is connected to the cylinder chamber  17 B. This supplies the pressurized drive air to the chamber  17 B and drives the piston  18  leftwardly. The control valve  73  also defines a second flow path  92  which is connected with the port  82  and connected with the discharge port  85 . Since the port  82  is connected to cylinder chamber  17 A, this allows the chamber  17 A to exhaust or depressurize the air from this chamber  17 A during the leftward movement of the piston  18 . Notably, the other exhaust port  83  is blocked as indicated by symbol  93 . 
         [0042]    As the piston  18  reaches its leftward end or limit of the leftward drive stroke, the controller  73  signals the control valve  73  to switch to the other operative position of the spool  88  which then reverses the operation of the drive cylinder  12  and causes the piston  18  to reverse stroke and move rightwardly. More particularly, when the spool  88  is in the other operative position, a flow path  94  is connected between the intake  81  and the port  82  which port  82  is connected to the cylinder chamber  17 A. This supplies the pressurized drive air to the chamber  17 A and drives the piston  18  rightwardly. The control valve  73  also defines a second flow path  95  which is connected with the port  84  and connected with the discharge port  83 . Since the port  84  is connected to cylinder chamber  17 B, this allows the chamber  17 B to exhaust or depressurize the air from this chamber  17 B during the rightward movement of the piston  18 . Notably, the other exhaust port  85  is blocked as indicated by symbol  96 . 
         [0043]    In this manner, the control valve  72  alternatingly switches between the two operative positions to selectively pressurize and exhaust the cylinder chambers  17 A and  17 B and thereby reciprocate the drive piston  18  and in turn drive the boost cylinder  14 . In this regard, the controller  73  is connected to the control valve  72  by the signal line  100  which is energized to actuate the solenoid  87  and drive the spool  88  to the second operative position which causes the drive piston  18  to move leftwardly. The control system also includes first and/or second feedback sensors  101  and  102  which connect to the controller  73  by sensor lines  103 . The feedback sensor(s) serve as proximity sensors which detect the position of the piston  18  as it approaches the end walls  19  and  20 . The feedback sensors  101  and  102  can be a variety of proximity sensors such as magnetic positioning sensors, accelerometers, pressure transducers, velocity sensors or vibration sensors which are capable of identifying the approach of the piston  18  towards one end wall  19  or the other end wall  20 . 
         [0044]    As the piston  18  moves leftward to the end wall  19 , the sensor  101  signals the controller  73  and the controller  73  deactivates the solenoid  87 , such that the return spring  89  returns the spool  88  to the initial, operative position. As such, drive air is now supplied to the cylinder chamber  17 A while the other chamber  17 B exhausts which allows the piston  18  to move rightwardly. Again, as the piston  18  reaches the rightward stroke limit, the sensor  102  signals the controller  73  to again actuate the solenoid  87  and switch the control valve  72  to reverse the piston stroke. 
         [0045]    These steps are then repeated as long as the controller  73  is instructed to run the booster cylinder  14 . The control process also automatically defines the speed of the unit by the controlling the pressurized air and drive cylinder  12 . As such, the controller  73  provides a cyclical power signal to the solenoid  87  and receives signals from the feedback sensors  101  and  102  to control the operation of the intensifier  10 . 
         [0046]    As an alternative to multi-sensor operation, only a single one of the sensors  101  or  102  may be provided wherein the one sensor  101  or  102  detects the proximity of the piston  18  at one end of the piston stroke and then the controller  73  cycles the piston  18  based upon that detection. For example, the one sensor  101  or  102  would detect the piston  18  at the one stroke end and reverse its movement, wherein the controller  73  could operate the piston by timing the cycle of the piston  18 . As the piston  18  travels through its stroke, the controller  73  could automatically reverse the piston  18  at the other end of the piston stroke after a set period of time, and then at the one stroke end detected by the sensor  101  or  102 , the controller  73  would again reverse the stroke based upon the proximity sensor signal. 
         [0047]    The system of the invention provides various advantages over the prior art. For example, the system provides a reliable booster for supplying the buffer gas after long periods of downtime for a compressor or other equipment. Also, the controller  73  is remotely operated and monitored, and is programmable to provide timed, variable duty cycles. The optimized cycle rate reduces drive air consumption to extend the operating life of the entire system. 
         [0048]    Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.