Abstract:
Pumps for Steam Condensates and other Liquids, include receivers that may be connected firstly to the liquid source, and after filling are then pressurised to discharge the liquid to a transfer line, or to a vessel at a higher pressure than that of the source. The use of a small pilot valve to detect the liquid level, mounted externally to each receiver, and controlling the opening and closing of the pressurising and venting valves, enables an unusually low profile to be achieved.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application 60/389,932 filed Jun. 20, 2002; British patent application 0214231.3 filed Jun. 20, 2002; and PCT/GB 2003/002276 filed Jun. 20, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to pumps for liquids and in particular, although not exclusively, to pumps for steam condensate. 
     Pumps utilising chambers that may be allowed to fill by gravity to a chosen level and that are then pressurised using either the vapour of the liquid being pumped, or air (or sometimes an inert gas), to push the liquid from the chamber, are often described as “pressure-powered” pumps. The liquid enters and leaves the chamber through “non-return” or “check” valves. At the top of the chamber are two much smaller valves. The first one of these admits the pressurising or “motive” gas when it is open. The second one is a vent valve for releasing the motive gas from the chamber. The motive gas valve and the vent valve may be pneumatically actuated. In the case of one pattern presently used, the pneumatic signals to the valve actuators are controlled by electrical level probes in the chamber. Alternatively, the two valves may be actuated by electric motors or solenoids, these again responding to electric level probes or level switches. 
     Other pressure-powered pumps in use at present, such as the pump  1  illustrated in  FIG. 1 , have a relatively large float  2  carried on a lever arm  4  within the chamber  6 . As the chamber fills with liquid, the buoyancy of the float  2  acting on the lever  4  applies force to one or more springs  8  which store energy as the float rises. At the upper tripping point the energy stored in the springs  8  is applied to a pushrod  10 . This moves in such a manner as to close the vent valve  12  and to open the motive gas valve  14 . The pressure in the chamber  6  then rises, closing the condensate inlet check valve  16 , and at a sufficient value discharging the condensate through the outlet check valve  18 . 
     As the condensate level in the chamber  6  falls, the float  2  is lowered, and its weight acting on the lever arm  4  again applies force to the springs  8 . At the lower tripping point, the mechanism trips in the reverse manner and the energy stored in the springs  8  is applied to the push rod  10  in the opposite direction, so as to close the motive steam valve  14  and open the vent valve  12 . The chamber pressure then falls as the motive steam is released and the next cycle begins. During the “discharge” phase of the cycle, condensate cannot enter the chamber, so a receiver is needed to accept and store the condensate until it can flow into the chamber at the start of the next cycle. 
       FIG. 2  shows an example of a pump  1  and an associated receiver  20  accepting condensate from a heat exchanger  22 . Steam enters the heat exchanger  22  via a pipe  22 A. The receiver  20  often is of a volume comparable to that of the chamber  6 , and it is mounted at a height so as to permit gravity flow into the chamber at a desired rate. A trap  20 A is fitted between the heat exchanger and the receiver  20 . The drainage outlets  24  on the equipment from which the condensate is flowing must be at an even greater height to allow gravity drainage to the receiver  20  if the condensate is to flow when the source is at low or atmospheric pressure. 
     Condensate flow from the receiver  20  to the pump chamber  6  is intermittent, so the pipe sizes used often must be greater than those needed for continuous flow. Equally, flow in the delivery pipe  26  from the pump  1  occurs only during the discharge phase, so the instantaneous flow rate is higher than the average rate. Often increased pipe sizes are needed, compared with those that would be adequate with continuous flow. 
     Such existing pumps can be effective but have several drawbacks. First, they are inherently intermittent in action, requiring over-sizing of associated pipe work. Second, the pump chamber must be sufficiently tall to provide enough movement of the float, which also needs to be large itself, so that enough operating power is obtained to open and close the motive steam and venting valves against the pressures being used. Furthermore, the receiver must be at a sufficient height to allow gravity drainage to the pump chamber, and so steam-using equipment and steam traps often must be higher still. This can increase the costs involved in mounting the steam-using equipment at sufficient elevation or, where equipment is already installed, may preclude drainage to the pump of condensate. 
     Another disadvantage associated with existing pumps is that the operating power of the mechanism is stored in one or more springs that are highly stressed. The springs are compressed or extended and released twice during each cycle of the pump, and are subjected to the severe conditions that exist within the operating chamber of the pump. Any replacement of a failed spring can only be effected after removal of the mechanism from the pump chamber. Similarly, removal of the mechanism from the pump chamber is needed before any maintenance work needed on other parts of the mechanism can be performed, or re-adjustment of the settings of the tripping levels. If any electrically operated probes, controllers or motors are used then these require special protection in locations that are dirty, steamy, or where inflammable vapours may be present. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided pump apparatus including: 
     a first container including a chamber, an inlet and an outlet, the chamber being pressurisable to effect discharge through the outlet; 
     a control apparatus for causing periodic pressurisation and depressurisation of the chamber in response to the level of liquid in the container, 
     wherein the control apparatus includes a pilot valve located in a second container connected to receive liquid from the first container when the level of liquid in the first container reaches a predetermined level, the pilot valve being configured to trigger a pressurisation/depressurisation cycle in response to the liquid level in the second container. 
     The outlet will normally include a non-return valve. During pressurisation motive gas enters the container, thereby causing the pressure of the liquid to exceed the outlet valve threshold. A shuttle valve may be used to allow the motive gas to enter or be vented from the container. 
     The second container can be relatively small compared with the first container. The second container may have its base at a relatively higher location than the base of the first container. The first and second containers may be linked by a pipe or line having a non-return valve. 
     The apparatus may further include a compressed air supply. The compressed air may be used as the motive gas. In an alternative embodiment, steam is used as the motive gas. In one embodiment, the compressed air is supplied to or vented from one or more thruster cylinder which operates to supply or vent steam (or any other suitable gas or vapour) for pressurisation/depressurisation of the container. 
     The pump apparatus may include two pumps substantially as described above, the apparatus further including a further valve component connected to a line for venting the motive gas from the containers of each pump, the further valve configured to open the venting valve of one pump when the venting valve of the other pump is closed. 
     According to a second aspect of invention there is provided pumping apparatus including two pumps, each said pump respectively including: 
     a first container including a chamber, an inlet and an outlet, the chamber being pressurisable to effect discharge through the outlet; 
     a control apparatus for causing periodic pressurisation and depressurisation of the chamber in response to the level of liquid in the container; the apparatus being arranged so that when one said pump is discharging liquid, the other pump is receiving liquid through its inlet. 
     Pumps according to the invention can be suitable for pumping liquids that may be unsuitable for pumping by the use of centrifugal or other rotating pumps, or may be used in locations where electrically powered or controlled pumps would be undesirable or hazardous. The two pumps may be connected together by means of a further valve component having an automatic valve in the inlet line of each said first chamber, the valves arranged such that when the chamber of one said pump is discharging, the other said pump is receiving liquid through its inlet. 
     Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be performed in various ways, and, by way of example only, embodiments thereof will now be described, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a side view of a conventional pressure-powered pump; 
         FIG. 2  illustrates schematically the pump of  FIG. 1  being used to pump heat exchanger condensate; 
         FIG. 3  is a side view of a first embodiment of a pump according to the present invention; 
         FIG. 4  is side view of a second embodiment where steam is used as the motive gas; 
         FIG. 5  illustrates schematically a third embodiment having a duplex arrangement; 
         FIG. 6  is a schematic perspective view of the pump of  FIG. 5 ; 
         FIG. 7  is a cross-sectional view through line A-A′ of  FIG. 4 ; 
         FIG. 8  is a schematic view of a further embodiment where piston-operated valves are used; 
         FIG. 9  is a plan view of part of the pump apparatus shown in  FIG. 8 ; 
         FIG. 10  is an end view of the apparatus of  FIG. 8 , and 
         FIG. 11  is a schematic perspective view of the apparatus of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 3  shows an embodiment of the pump  300  where compressed air is used as the motive gas. The liquid to be pumped flows from a receiver tank (not shown) through a high-level non-return valve  302  into a chamber  304 . The valve  302  is located near the top of the chamber  304 . In the embodiment of  FIG. 3  the chamber is also connected to a second non-return valve  305  by a pipe that is located near the base of the chamber  304 . 
     In an alternative embodiment, a “dip” pipe  305 A passes through the top of the chamber  304  to near the bottom of the chamber, the valve  305  being located above the top of the chamber. This arrangement can allow the liquid level in the chamber  304  to fall to a lower level. The possible dip pipe  305 A and valve  305  are shown within the line  3 A in  FIG. 3 . 
     The valve  305  is intended to act as an outlet. A vent pipe arrangement  307  is connected to the upper portion of the chamber  304  which is intended to allow gas in the chamber to be vented as liquid enters. The chamber  304  is connected to a substantially horizontal pipe  308  (of ½″ or 15 mm nominal size) fitted with a non-return valve  312 . The valve  312  can be of the swing check pattern or another type opening to a similar head of liquid. A vertical pipe  311  leads from the pipe  308  to a pilot valve chamber  310  which is relatively small compared with the main pump chamber  304 . The chamber  310  may be cuboid or cylindrical in shape or it may be shaped as shown in the Figure. The chamber  310  contains a small float  316  attached to a valve  318 . 
     A compressed air supply at location  320  is connected to a line  322  having a T-junction  324 . One branch of the junction leads down to a line  326  connected to the valve  318 . The line  326  incorporates an orifice restrictor  328  having a pass area much less than that of the valve  318 . The pressure between  328  and  318  in line  326  downstream of restrictor  328  and upstream of valve  318  may be at least ⅔ to 1 bar below supply pressure when the float valve  318  is open (an orifice diameter of 2 mm through which a split pin is fitted can function satisfactorily). 
     The other branch of the junction  324  leads to a line that is fitted with a T-junction  332 . One branch  334  of the junction  332  passes through a small pressure regulator valve  336  to one port  338  of a three-port shuttle valve  340 . The opposing port  339  is connected to a part of the pipe  326  below the orifice fitting  328 . The pilot port  338  is subjected to an air pressure that is maintained by the regulator valve  336  at a level around ½ bar less than the maximum pressure at the port  339 . The valve  340  is connected to the chamber  304  and can switch between a first position where gas in the chamber can pass out through a vent  306  and a second position where compressed air can enter the chamber via a second branch  342  of the T-junction  332 . 
     Operation of the pump  300  will now be described. The liquid to be pumped flows through the high-level non-return valve  302  into the chamber  304 . At this point air in the chamber  304  can be displaced through the vent line  306 . Liquid in the chamber is allowed to flow through the horizontal pipe  308  towards the pilot valve chamber  310 . The liquid cannot pass in this direction through the non-return valve  312 . When the liquid in the chamber  304  has reached a sufficiently high level it can overflow through the vertical pipe  314  into the chamber  310 . The liquid surface area within chamber  310  is much less than that in chamber  304  and so the rate at which chamber  310  fills is very rapid compared with the slower progressive filling of chamber  304 . When the liquid level in the chamber  310  is sufficiently high the float  316  is moved to open the valve  318 . Air from line  326  then flows into the pilot valve chamber  310  and the main pump chamber  304 . Thus, the pressure in pipe  326  is lowered, causing the shuttle valve  340  to change over and apply motive air. 
     In steam/condensate applications, the use of steam as the motive gas is often desirable, and a pump arrangement  400  such as that shown in  FIG. 4  may be applicable. Parts substantially similar to those of the embodiment of  FIG. 3  are given identical reference numerals and will not be described in detail again. Motive steam passes through a Wye strainer  401  and is admitted to the chamber  304  through a quarter-turn ball valve  402 . The valve can be as small as ¼″ or 7.5 mm nominal size for condensate loads of up to about 5000 Liters per hour. A vent valve  404  is a similar ball valve of ½″ or 15 mm nominal size. The operating levers  409  of the valves are turned by the action of one or more pneumatic “thruster” cylinders  410  of the spring return type that are supplied with compressed air, or are vented, through a shuttle valve  340  substantially as previously described. 
     In steam/condensate applications, the use of steam as the motive gas is often desirable, and a pump arrangement  400  such as that shown in  FIG. 4  may be applicable. Parts substantially similar to those of the embodiment of  FIG. 3  are given identical reference numerals and will not be described in detail again. Motive steam passes through a Wye strainer  401  and is admitted to the chamber  304  through a quarter-turn ball valve  402 . The valve can be as small as ¼″ or 7.5 mm nominal size for condensate loads of up to about 5000 Liters per hour. A vent valve  404  is a similar ball valve of ½″ or 15 mm nominal size. The operating levers  409  of the valves are turned by the action of one or more pneumatic “thruster” cylinders  410  that are supplied with compressed air, or are vented, through a shuttle valve  340  substantially as previously described. 
     U-seals  406  are built into the pipe work so that steam cannot reach the shuttle valve pilot ports  338 ,  339 . The seals can sense the pressure of air trapped in a pipe  408  leading to the shuttle port  339 . 
     The operating levers  409  of the two ¼-turn ball valves  402 ,  404  may be linked together and operated by a single thruster  410 , or each may have its own thruster. Addition of an extra vent valve, as described below, enables a duplex arrangement to be adopted. 
       FIGS. 5 to 7  show diagrammatically such a duplex arrangement in a pump arrangement  500 . Again, substantially similar parts are given the same reference numerals as in the earlier embodiments. The pump  500  includes two chambers  304 A,  304 B, each chamber having its own associated components labelled with a suffix A or B. Descriptions of parts or operations will not be duplicated herein where it is apparent from the Figures that two corresponding components exist. Each chamber has its own thruster cylinder  410 . Preferably, the cylinder  410  is of the single acting, spring return pattern, although a double-acting cylinder could be used. Each cylinder  410  operates a motive steam valve  402  and an initial venting valve  404 . Each cylinder  410  has a respective controlling shuttle valve  340 , each responding to the pressure in pipe  326  substantially as described previously. The initial venting valve on each chamber discharges through a non-return valve  504 . This offers a slight resistance to flow, by the weight of the valve disc. Alternatively, the disc may be spring-loaded. 
     An extra vent valve  506  is fitted in a bypass around each non-return valve  504 . Both valves  506 A,  506 B for both of the chambers  304 A,  304 B are operated by one double-acting thruster  508 . The valves are arranged so that if either valve is closed, then the other valve is opened to complete the venting of its respective chamber. Each end of the thruster  508  is supplied with air at the same time as the respective thruster  410  that opens the steam supply valve on one of the pumping chambers. When one chamber has filled with condensate, its float pilot valve  318  is opened and the pressure in its pipe  326  is lowered. The shuffle valve  340  admits air to the thruster  410  and moves the steam valve to “open” and the initial vent valve  404  to “closed”. The double-acting thruster cylinder  508  closes the vent valve  506  on this chamber and opens the vent valve  506  on the second chamber. The second chamber can then fill. 
     When the contents of the first chamber  304 A have been pumped down to the “empty” level, the float pilot valve  318 A closes. Pressure in the pipe  326 A increases, changing the position of the shuttle valve  340 A. The valve  340 A vents the thruster  410 A which closes the steam inlet valve  402 A, and opens the initial vent valve  404 A. Air is vented also from thruster  508 , but the piston does not move, as both ends of the cylinder are now vented. The two vent valves  506 A,  506 B remain closed and open, respectively, and the first chamber  304 A retains sufficient pressure so that its inlet check valve  302 A remains closed. Only when the second chamber  304 B has filled does its pilot float valve  318 B open, so that its steam valve  402 B can open. Its vent valve  404 B closes and the vent valve  506 A of the first chamber  304 A opens. The first chamber can then refill, as the second chamber is pumped out. 
     Each of the chambers effectively acts as a receiver tank to accept condensate when the other chamber is discharging. The two chambers  304  are thus allowed to fill and discharge alternately, making the flow of condensate to the pump virtually continuous, and discharge of the condensate into the delivery pipe may be more nearly continuous than when a single chamber is used. As no receiver tank located above the pump is needed, the apparatus requires less height than conventional arrangements. Further, the pump chamber need not usually contain any moving parts and so requires minimal maintenance. 
     When the pressure of the motive steam is reasonably constant, the pressure of the air supplied to the pilot port of the shuttle valve opposite to the one sensing the conditions in pipe  326  is set by adjustment of the control spring of a standard pressure-regulating valve  336 . Alternatives that could be used if the steam pressure is subject to variations in a particular installation include: 
     a) replacing the adjustment spring of the regulator with a pressure tight housing, and connecting the steam pressure to this. A light return spring below the diaphragm would be chosen so that the valve controlled the air pressure to about ½ bar below the steam pressure. 
     b) Using an extended pilot valve cover on that end of the shuttle valve connected to pipe  326  to allow the use of a small spring, to bias this end of the shuttle by the equivalent of ½ bar pressure. Instead of using an air pressure regulator, the pressure of the steam supply is applied through a U-seal to the opposing pilot. 
     Pressure-powered pumps of any type presently available, having large internal float mechanisms with springs to store energy, or using level switches or probes to control motorised valves, will each accept liquid from a large receiver mounted above them. To obtain sufficient pumping capacity to deal with larger loads, two of these pumps may be used in parallel, with a common receiver above them. The system including duplex pumps described above can be adapted to obviate the need for the receiver and to provide a somewhat lower profile unit. The vent, or exhaust line, from each pump can be simply fitted with a line size check valve having a spring-loaded valve disc. Each check valve can have a bypass pipe in which a ball valve is fitted. The two ball valves are operated by a common double-acting thruster cylinder as described above. This is supplied with compressed air through a 5-port shuttle valve, and the two pilot ports of the shuttle valve are each connected to points below the minimum water level in the respective pumps. 
     When the motive steam valve on either pump chamber is open, the pressure on the liquid is then sensed at the 5-port shuttle valve. This changes position and the thruster opens the ball valve in the vent line of the other pump. The two pumps then operate alternately, and one chamber is always available to accept liquid while the other pump is emptying. 
     It is desirable that the float chamber  310  fills as quickly as possible when the level of the pumped liquid has reached the top of the vertical pipe  314 . To this end, the pipe  314  can be connected into a section of pipe of greater diameter, itself containing a central vertical overflow pipe. The end of this overflow pipe can be a 25.4 mm or 1″ nominal bore pipe socket. The rim of this socket can have a circumference of around 127 mm or 5″, over which liquid can overflow much faster than through a 12.7 mm or 0.5″ horizontal nominal bore pipe. 
     In another alternative embodiment of the invention, the quarter-turn ball valves  402 / 404  are replaced with piston-operated on-off valves, e.g. Spirax Sarco PF61G NC/NO valves. The pistons may be operated by compressed air in the same way as the thruster valves described above. The embodiment of  FIGS. 8 to 11  incorporates such valves  800 A/B,  801 /AB which are actuated by water pressure. 
     The two steam pressures that may be present between the fixed orifice  328  and the float-operated valve  318  are connected to a chamber  802  that replaces the u-seal  406 . The chamber  802  may simply be a length of about 100 mm or 4″ of 50.8 mm or 2″ nominal bore pipe and is filled to an appropriate level with water. The cylinders of the piston-actuated valves  800 ,  801  are connected to the chamber  304  by pipes so that the control pressures are transmitted to them by water pressure. The motive steam supply valve  800  is of the “normally-open” pattern and the vent valve  801  is “normally-closed”. 
     When the float-operated valve  318  is closed, full motive steam pressure is applied to close the steam valve  800  and open the vent valve  801 . Opening of the float-operated valve  318  when the pumping chamber  802  is full lowers the pressure in the chamber and this is applied to the actuating pistons  800 ,  801 . The valve  803  can be used to assist in completing the venting of the chamber and remove any residual pressure. The chamber vent valve  801  then closes and the motive steam valve  800  opens. 
     In another embodiment the two pumps may be connected together by means of a further valve component having an automatic valve which is fitted in the inlet line of each chamber  304 A,  304 B (normally before the inlet valve  302 ). The automatic valve can operate such that when the chamber of one pump is discharging, the other pump is receiving liquid through its inlet.