Abstract:
A pump assembly comprising an apparatus for reducing process noise manifest in a piping system. The invention introduces a pump pulse to counteract a negative dip in pressure when the reciprocating pump is at the completion of each pump stroke.

Description:
FIELD OF THE INVENTION 
     The invention relates to a reciprocating pump assembly, a noise suppression apparatus for use with a reciprocating pump, and a method of controlling a reciprocating pump assembly. 
     BACKGROUND 
     One of the most common air-operated pumps used in industry is a double-diaphragm, positive displacement type shown in  FIG. 1 . This type of pump is self-priming and displaces fluid from one of its two liquid chambers upon each stroke completion. Only several parts contact the fluid, two diaphragms which are connected by a common connecting rod, two inlet valve balls, and two discharge valve balls. The diaphragms act as a separation membrane between the compressed air supply operating the pump (air chamber) and the liquid (fluid chamber). Driving the diaphragms with compressed air instead of the connecting rod balances the load on the diaphragm, which removes mechanical stress and extends diaphragm life. The valve balls open and close on valve seats to direct liquid flow. When each diaphragm has gone through one suction and one discharge stroke, one pumping cycle has taken place. An air distribution system is part of the pump and switches the common air supply for the pump from one air chamber to the second air chamber as each fluid chamber empties at the end of its respective stroke. 
     The air distribution system shifts the symmetric pumping action in order to create suction and discharge strokes. When the diaphragms have traveled a maximum excursion in one direction, a mechanical pilot valve is typically actuated, shifting a main valve, and reversing the pneumatic action. The other air chamber is then pressurized to expel its fluid and the device continues this reciprocation until the air supply is stopped. Various pump manufacturers accomplish the air distribution using purely mechanical valve assemblies and/or valve assemblies that are electrically controlled. 
     The discharge of a double-diaphragm, reciprocating pump is dependent only on the mechanical characteristics of the air distribution system and the fluid dynamics of the pump itself. Shown in  FIG. 2  is a typical discharge pressure versus time plot of a prior art, dual-diaphragm, air-operated pump.  FIG. 3  shows the corresponding plot of the air distribution system connecting rod excursion in time, as the rod travels in the direction of one diaphragm pump, arbitrarily denoted as left, then to the other diaphragm pump, arbitrarily denoted as right. As the diaphragms complete their travel in one direction and reverse direction, a large pressure dip occurs when the connecting rod is at the excursion limit. This is due to the inherent pressure change when transitioning between suction and discharge strokes. The output results in a series of pulses or surges corresponding with each diaphragm pump stroke. In the control systems art, these surges manifest in the process piping are referred to as process noise. All pumps operating with some type of reciprocation produce process noise. 
     To reduce unwanted fluctuation, passive external pulsation dampeners can be added downstream of the pump. The prior art dampener shown in  FIG. 4  contains a pressure regulator and a pressurized diaphragm acting as an accumulator. The diaphragm traps a given volume of liquid on one side and pressurized air on the other. When the fluid pressure falls in the system, the dampener supplies additional pressure to the discharge line between pump strokes by displacing fluid by the diaphragm movement. This movement provides a supplementary pumping action needed to minimize pressure variation and pulsation. Most dampeners set and maintain air pressure to match the variations in the liquid flow or discharge pressure generated by the pump. A shaft attached to the diaphragm and pressure regulator triggers the addition or deletion of the air within the air chamber side of the dampener. The dampener reacts to pressure and/or flow settings of the pump with no need for manual adjustment. 
     However, the prior art external pulsation dampeners are large and require additional support, making them costly to purchase and install. By their passive nature, these dampeners are slow to react and process noise is still introduced into the system as shown in  FIG. 5 . 
     What is needed is a low cost, active suppression device to anticipate and cancel process noise produced by reciprocating pumps thereby reducing water hammer and strain on equipment coupled downstream. 
     SUMMARY 
     The invention provides, in one embodiment, an apparatus for canceling process noise introduced by a reciprocating pump. In one construction, the apparatus includes a controller corresponding with a reciprocating pump connecting rod, the controller adapted to output a signal during each connecting rod excursion. The signal is coupled to a solenoid valve, which opens to admit an air supply to operate a pulse pump having a discharge coupled to the reciprocating pump discharge. The pulse pump ejects a predefined quantity of fluid when the solenoid valve is opened. 
     In another embodiment, the invention provides a rate sensor adapted to receive inputs from a reciprocating pump and output a signal representative of device rate to a controller. The controller processes the device rate signal as process noise manifest by the reciprocating pump and outputs an anti-noise signal to a pulse pump whereby the anti-noise signal is an inverted replica of the device noise. The pulse pump output is coupled to the reciprocating pump discharge and outputs a pressure profile corresponding to the anti-noise signal thereby canceling the process noise manifest by the pump. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front, section view of a prior art double-diaphragm, reciprocating pump. 
         FIG. 2  is a plot of discharge pressure versus time for the pump shown in  FIG. 1 . 
         FIG. 3  is a plot of connecting rod excursion versus time for the pump shown in  FIG. 1 . 
         FIG. 4  shows a prior art surge dampener coupled downstream of a double-diaphragm, reciprocating pump. 
         FIG. 5  is a plot of discharge pressure versus time with the surge dampener of  FIG. 4 . 
         FIG. 6  is a schematic diagram of a double-diaphragm, reciprocating pump assembly incorporating the invention. 
         FIG. 7  shows the physical application of the pump assembly of  FIG. 6 . 
         FIG. 8  is a plot of connecting rod excursion versus time for the pump assembly of  FIG. 6 . 
         FIG. 9  is a plot of pulse pump discharge pressure versus time. 
         FIG. 10  is a plot of discharge pressure versus time for the pump assembly of  FIG. 6 . 
         FIG. 11  is a schematic diagram of an alternative construction of the double-diaphragm, reciprocating pump assembly incorporating the invention.  FIG. 12  is a schematic diagram of another alternative construction of the double-diaphragm, reciprocating pump assembly incorporating the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Before any aspects of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     Shown in  FIGS. 6 and 7  are schematic and physical diagrams of one construction of a double-diaphragm, reciprocating pump assembly. Before proceeding further, it should be noted that while a double-diaphragm, air operated pump is shown for  FIGS. 6 and 7 , the invention may be used with other types of reciprocating pumps regardless of the motive power. 
     By way of background, the examination of process noise is typically performed in the frequency domain. Namely, how the noise energy is distributed as a function of frequency. Turbulent noises distribute their energy evenly across the frequency bands and are referred to as broadband noise. Narrow band noise energy is concentrated at specific frequencies. When the source of noise is a rotating or repetitive machine, the noise frequencies are all multiples, or harmonics, of a basic noise cycle. This type of noise can be classified as periodic, along with a smaller amount of broadband noise and is common in man-made machinery. Examples of sources of narrow band noise include internal combustion engines, compressors, power transformers and pumps. 
     Shown in  FIG. 6  is an assembly  15  arranged to cancel the noise manifest in process piping by an air-operated, reciprocating pump  17 . The assembly  15  includes a controller  19  and connecting rod position transducer  21  mounted adjacent to a connecting rod  23  of the air-operated, reciprocating pump  17 . The pump  17  receives its motive power from a common air supply  25 . 
     The connecting rod position transducer  21  corresponds with the common connecting rod  23  coupling each diaphragm  27 ,  29  on the pump  17 . The transducer  21  monitors the excursion of the connecting rod  23  using a sensor. The sensor can be reed, proximity, or other equivalent limit switch types. The sensor can also be a linear displacement device such as a digital gauging probe, a linear variable differential transformer (LVDT), a hybrid micro-electromechanical system (MEMS), or other like equivalents. The linear displacement sensor similarly corresponds with the connecting rod. The rod position transducer  21  output is communicated to the controller  19 . 
     As the connecting rod  23  nears its excursion limits at each end of travel, a signal based on the connecting rod  23  location is output from the controller  19  to a solenoid valve  31 . The solenoid valve  31  controls the air supply  25  to a pulse pump  33 . Upon energization, the solenoid valve  31  opens, admitting air to the pulse pump  33 . The pulse pump  33  has a predefined volume on a fluid side of a diaphragm, which is ejected, into the pump  17  discharge. 
     Shown in  FIGS. 8 and 9  is the timing of the solenoid valve  31  openings and the output pressure response of the pulse pump  33  respectively. The pulse pump  33  discharges before the excursion limits are reached by the connecting rod  23  to allow the fluid inertia to produce a positive pressure in the pump discharge and cancel the pump  17  pressure dips as shown in  FIG. 10 . 
     The assembly  15  allows for either maintaining, advancing, or retarding pulse pump  33  operation depending upon speed of the pump  17 . The controller  19  monitors the connecting rod  23  position via the rod position transducer  21  and, by counting the cycles per unit time, arrives at pump  17  speed and discharge volume. The operation of the pulse pump  33  is timed during the connecting rod  23  excursion to maximize noise suppression. At slow pumping speeds, pulse pump  33  actuation is retarded, occurring later during the connecting rod  23  excursion. At faster speeds, pulse pump  33  actuation is advanced, occurring earlier during the excursion. 
     In an alternative construction, the assembly  15 B reduces reciprocating pump  17  process noise by generating a canceling, anti-noise signal, which is an inverted replica (180° out of phase) of the noise manifest in the process line. The anti-noise signal is then introduced into the noise environment via the pulse pump  33 . The two noise signals cancel each other out, effectively removing a significant portion of the noise energy from the process. 
     The technique of synchronous feedback is effective on repetitive noise. An input signal is used to provide information on the rate of the noise. Since all of the repetitive noise energy is at harmonics of the pump cyclical rate, a digital signal processor can cancel the known noise frequencies. Digital signal processors (DSPs) perform the calculations involved in noise cancellation. The use of DSPs makes it feasible to apply active noise cancellation to problems in low frequency noise at a reasonable cost.  FIG. 11  shows active noise cancellation applied to the assembly  15 B to reduce the process noise attributed to pump discharge pulsing. The active element is the pulse pump  33 . The pulse pump  33  outputs an anti-noise pulse to the pump  17  discharge. The process noise profile and anti-noise provides for global cancellation of the low frequency process noise. 
     The connecting rod transducer  21  outputs a signal representative of pumping rate. The signal is coupled to a generator  35  to internally provide frequencies at the harmonics of the pump  17  rate. The rate is modeled by the connecting rod travel  23  (excursion) versus time. The excursion establishes the fundamental frequency of the noise and any acceleration or deceleration the connecting rod  23  may experience during each stroke. 
     The generator  35  artificially models the noise estimate. The noise estimate is output and coupled to the input of a programmable filter  37  such as a finite impulse response filter (FIR). Other embodiments may use infinite impulse, Kalman, or equivalent filter structures. The filter  37  builds a mathematical representation of the noise estimate having a gain equal to the noise and a phase shift of 180°. The output is a new signal approximating the expected noise in the process. The new signal is used to cancel the noise and is the basic tenet of feed forward control. 
     The cancellation signal is amplified  39  and output to a modulating valve  31  for transducing the cancellation signal to air pressure for operating the pulse pump  33 . The operation of the pulse pump  33  cancels the narrowband noise effects of the mechanical pumping cycle. 
     Another alternative construction of the assembly  15 C having a feed forward control system is shown in  FIG. 12 . The assembly  15 C further includes an adaptation scheme to adapt the programmable filter  37  to further minimize error. Considering the importance of gain and phase matching in feedforward control, this variant implements adaptive algorithms such as a least mean square (LMS) algorithm to minimize errors in these parameters based on minimizing the mean square of the disturbance response. Other schemes such as a filtered-x least mean square (FxLMS) algorithm may be used. A pressure sensor  43  in the discharge of the pulse pump  33  feeds back noise remaining after cancellation to an adapter  45 . The adapter  45 , using an LMS adaptation algorithm, continuously adjusts the cancellation filter  37  to drive any remaining process noise to zero. 
     Accordingly, the invention provides new and useful pump assemblies, suppression apparatus for use with a pump, and methods of controlling a pump assembly. Various other features and advantages of the invention are set forth in the following claims.