Abstract:
A sprinkler system for building includes an internal combustion engine which operates a water pump. The water pump in turn forces water through pipes to sprinkler heads. The engine is at least in part controlled by a throttle control mechanism which includes a spring biased piston which is moved in response to the output pressure of the pump. This prevents the pump from exceeding the rated pressure of the system components.

Description:
RELATED APPLICATIONS 
   This application is a continuation in part of U.S. patent application Ser. No. 10/142,206, filed on May 9, 2002, by John Whitney, titled “Pump Pressure Limiting Engine Speed Control, which application is now abandoned. 

   BACKGROUND OF THE INVENTION 
   Building sprinkler systems are designed to provide pressurized water to extinguish fires during emergency situations. A pump is used to provide the necessary water pressure. These pumps are typically powered by an electric motor, however many are often powered by internal combustion engines. The present invention relates to internal combustion engine systems only. 
   Such sprinkler systems are designed for a defined flow rate and pressure. For a given engine/pump combination, the discharge line pressure, from the pump, is dependent on the fluid flow rate through the system and the pressure of the water being supplied to the pump (called suction pressure). The pressure of the water at the pump suction often has a wide range between its high and low resulting in an equally wide contribution to pump output pressure variances. At a constant engine/pump RPM (Revolutions Per minute). The line pressure will increase as the fluid flow rate decreases through the system. Further, at a fixed throttle setting, as the fluid flow rate decreases, the load on the engine also decreases resulting in an increase in engine rpm, thereby further increasing pressure produced by the pump (this is referred to as the engine droop). The net effect is to increase the pressure, which a sprinkler system must be able to withstand. This basically means stronger more expensive sprinkler system components including water pipes, fittings and sprinklers. Sprinklers are rated for specific operating pressures. This establishes the limits of the system pressures. Some types of sprinklers are further limited to smaller more specific pressure ranges further limiting system pressure ranges. 
   SUMMARY OF THE INVENTION 
   The present invention is premised on the realization that the need for higher pressure rated sprinkler systems can be avoided by utilizing an engine throttle control which is responsive to the output pressure of the pump. As the pump pressure increases above a defined pressure, a control mechanism is utilized to retard the throttle, thereby reducing engine RPM and in turn maintaining a relatively constant system pressure. 
   Preferably the control mechanism is a piston which is attached to the throttle and forced in a direction that retards the throttle when water pressure is increased beyond a given limiting pressure. The piston is spring biased so that when the system pressure decreases, the throttle will return to its normal setting to operate the pump within design parameters. Knowing the pressure at the rated flow of the pump allows one to adjust the control mechanism to maintain this pressure even at low flow rates thereby eliminating the need for the more expensive plumbing created by undesirable pressure. 
   The objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  presents a pictorial view of a typical internal combustion engine driven pump installation as typically used in a fire prevention sprinkler system. 
       FIG. 2  presents a schematical diagram illustrating a preferred engine speed control system and its pertinent operating elements 
       FIG. 2A  presents an alternate arrangement for the overpressure control valve which is hydraulically controlled. 
       FIG. 3  presents a comparison of the fluid pressure necessary to obtain a given throttle movement for the two embodiments of the present invention presented herein 
       FIG. 4  presents an alternate embodiment of the present invention wherein the engine throttle is set at full throttle 
       FIG. 5  presents the alternate embodiment of the present invention, illustrated in  FIG. 4 , wherein the engine throttle has been retarded by present invention illustrated in  FIG. 4 . 
       FIG. 6 . presents typical system performance of flow versus system pressure and flow versus engine RPM when a throttle control mechanism is not installed on the engine. 
       FIG. 7 . presents typical system performance of flow versus system pressure and flow versus engine RPM when a throttle control mechanism is installed on the engine. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Preferred Embodiment of The Present Invention 
     FIG. 1  presents a pictorial view of a typical internal combustion engine  22  coupled to a typical fire prevention sprinkler system pump  14  that is suitable for application of the present invention. 
   As shown in  FIG. 1 , sprinkler system  12  includes a pump  14  which directs water from the pump inlet, or suction, pipe  18  and through outlet pipe  16  to sprinkler heads (not shown). The pump  14  is in turn operated by internal combustion engine  22 , preferably a diesel engine. Engine  22  drives shaft  24  which in turn operates pump  14 . 
   The RPM of engine  22  and thereby shaft  24  is controlled by throttle lever  26 . Throttle lever  26  is operatively connected to a control mechanism, which is mounted on engine  22  by bracket  32 . The elements of control mechanism  28  and its functional operation are described below. 
   Turning now to  FIG. 2 , throttle control mechanism  28  comprises a throttle control actuator assembly  30  fabricated from an open ended cylinder  35 . A first end block  38  closes off and seals the first end of cylinder  35 . A second end block  39  closes off and seals the opposite end of cylinder  35 . A slidable piston  34  is received within cylinder  35  as illustrated in  FIG. 2 . Compression spring  44  extends from end block  38  to piston  34  thereby biasing piston  34  against shoulder  42  of end block  39  which corresponds to the full open throttle position. 
   Within end block  39  is fluid receiving chamber  46  A piston rod  45 , integral with piston  34 , extends axially through chamber  46  extending beyond end block  39 , as illustrated in  FIG. 2 , and connects to throttle linkage  50 . Piston rod  45  is appropriately sealed by an O-ring  48  thereby preventing fluid linkage around the piston rod. 
   A fluid dampening reservoir  40  is attached to end block  38  via orifice  41  thereby fluidly communicating with cylinder  35  through fluid channel  52  within end block  38 . Orifice  41  functions to dampen fluid pressure surges in that may otherwise be transmitted directly to dampening reservoir  40 . 
   Fluid pressure is received within fluid chamber  46 , from tube  54 A, and acts upon slidable piston  34  thereby compressing spring  44  whereby piston rod  45  translates to the left, as viewed in  FIG. 2 , thereby rotating throttle lever  26  counterclockwise thereby retarding throttle lever  26 . 
   In operation, pump discharge pressure is received, from pump discharge  16 , in line  54 . Relief valve  58  is normally closed. However, if the pump discharge pressure exceeds the set point of relief valve  58 , which is calibrated to maintain normally 170 psi, but may range from 10 to 240 psi, in pump discharge line  16 , relief valve  58  opens thereby permitting fluid flow through line  54 A, control line  60 , exhaust valve  62 , and through orifice  66  into drain  64 . As fluid flows through orifice  66  a controlled back pressure is created in control line  60  and line  54 A communicating with fluid chamber  46  in throttle actuator  30 . Thus the pressure acting upon piston  34  is substantially reduced below the pump discharge pressure in pump discharge  16 . 
   At start up and/or during normal steady state operating conditions throttle  26  and the throttle control actuator assembly  30  are positioned as illustrated in  FIG. 2 . Compression spring  44  is biasing piston  36  and its associated piston rod  45  to the right as viewed in  FIG. 2 . In this configuration throttle lever  26  is positioned in its full open position whereby pump  14  is providing a predetermined water flow rate and working pressure at rated operating speed throughout the sprinkler system, not shown, by way of discharge pipe  16 . As the system is operating, the line pressure of discharge pipe  16  is also present in inlet tube  54 . So long as the pressure within discharge pipe  16  and inlet tube  54  is below a pre set pressure limit of relief valve  58 , typically 170 psi, relief valve  58  remains closed thereby preventing any fluid flow, or preventing enough flow against orifice  66  to create sufficient back pressure to produce movement of piston  34 , into inlet line  54 A that would overcome the bias from spring  44  to move the piston. Thus throttle control assembly  30  is unaffected and throttle lever  26  remains unchanged. 
   However, in the event line pressure in pump discharge pipe  16  and inlet tube  54  rise above the set limit of 170 psi, relief valve  58  opens thereby permitting fluid flow into inlet line  54 A. Fluid flow now occurs through inlet line  54 A and through control line  60 , to and through exhaust valve  62 , which is open to line  60 A. As the fluid flow passes through line  60 A, it passes through orifice  66  and into drain line  64 . Orifice  66  acts to restrict the fluid flow through control line  60  thereby causing a controlled back pressure throughout control line  60  and into chamber  46 , within throttle control assembly  30  by way of back pressure line  54 A. Thus the fluid pressure acting upon piston  34  is greatly reduced from that of discharge pipe  16 . Nevertheless as line pressure within discharge pipe  16  varies the back pressure caused by orifice  66  will also vary accordingly causing piston  34  to move against compression spring  44  thereby retarding and/or advancing throttle lever  26 . Once line pressure within discharge pipe  16  drops below the set point, relief valve  58  will close thereby preventing or reducing further fluid flow through control line  54 A,  60 ,  60 A and orifice  66 . Fluid pressure within the control lines will then decay to a pressure below the pressure required to overcome the bias of the spring  44  or to atmospheric, the pressure existent within drain  64 . Compression spring  44  will then bias piston  34  to the right, against shoulder  42  thereby resetting throttle lever  26  to its normal operating position. 
   Fluid damping reservoir  40 , fluidly communicating with cylinder  35  through conduit  52 , is preferably provided to dampen rapid fluid pressure fluctuations that may occur within control line  54 A, fluid chamber  46  and acting on piston  34 . 
   A further method of damping pressure fluctuations that may occur in control line  54 A is to place an orifice within control line  54 A between relief valve  58  and fluid chamber  46  and/or between valve  58  and pump discharge  16 . 
   During operation of the throttle control system  28 , pressure switch  68  constantly monitors the fluid pressure within control line  60 . In the event of orifice  66  becoming artifically restricted and the fluid pressure within control line  60  becoming artifically high, an electrical signal is transmitted through electrical connection  70  to three way exhaust valve  62  thereby opening the valve to relieve line  63  thereby dumping the fluid pressure within control line  60  and throttle control actuator assembly  30  causing piston  34  to be biased by spring  44  to the right against shoulder, thereby returning throttle  26  to its normal operating position. 
   However as illustrated by curve  75  in  FIG. 3 , by employing the preferred embodiment of the invention, as described above, the fluid pressure acting upon piston  36  has been significantly reduced to the back pressure value created by orifice  66 , within input lines  60  and  54 A, as fluid passes therethrough. Thus throttle control assembly  30  need not be designed to withstand operational fluid pressures of 170 psi and above 
     FIG. 3  presents a plot of the fluid pressure acting upon piston  34  as a function throttle movement, for a sprinkler system embodying the preferred embodiment of the present invention as described above, as compared to the fluid pressure acting upon piston  156  in the alternate embodiment of the present invention described herein below. Referring to  FIG. 3 , curve  75  represents a typical plot of the pressure acting upon piston  34  vs. throttle, or piston, movement and curve  70  typically represents the pressure acting upon piston  156  vs. throttle or piston movement in the alternate embodiment described below. As seen in  FIG. 3  the preferred embodiment of the present invention requires a greater pressure change, or delta P than the alternate embodiment represented by curve  70 . Therefore, the preferred embodiment of the present invention offers a more sensitive control of throttle movement than that offered by the alternative embodiment below. 
     FIG. 2A  presents an alternate system for exhaust valve  62  and its associated pressure sensing switch  68 . As illustrated in  FIG. 2A  exhaust valve  62  and pressure sensing switch  68  may be replaced by a typical, mechanically operated, pressure relief valve  63 . Thus the function of exhaust valve  62  and pressure sensing switch  68  may be replaced by a mechanical as opposed to an electrically functioning pressure relief system. 
   As illustrated in  FIG. 3 , the fluid pressure acting upon piston  156  in the alternate embodiment described below, represented by curve  70 , is equal to 170 psi or higher and equal to the line pressure of pump discharge- 16  immediately upon the opening of the relief valve  58  and continues to climb as discharge pressure  16  climbs. 
     FIG. 6  presents a plot of the fluid pressure versus flow, curve  86 , within pump discharge line  16  when the system is not present. As illustrated, the pump discharge pressure significantly exceeds the system pressure limit of approximately 175 psi. Curve  88  illustrates the associated engine/pump speed versus flow. 
     FIG. 7  presents a plot of the fluid pressure versus flow, curve  82 , within pump discharge line  16  when the system is activated to overcome a pump discharge pressure reaching or exceeding the set point of 170 psi. of relief valve  58 . As illustrated, the pump discharge pressure is relatively constant at about 170 psi. Curve  84  illustrates the associated engine/pump speed versus flow. 
   Alternate Embodiment of the Present Invention 
   An alternate embodiment to the preferred embodiment described above is illustrated in  FIG. 4 . As illustrated in  FIG. 4 , an alternate embodiment control mechanism  128  includes a piston  134  which extends through a block  136 . Rearwardly of block  136  is a cylindrical casing  138  which screws onto block  136 . Opposite block  136  is a cap  142  which screws onto the cylindrical casing  138  holding it in position. Between the cap  142  and the piston  134  is a spring  144  which engages a rear end  146  of piston  134 . 
   Piston  134  includes a shaft  148  having a threaded end  152 . The opposite end of piston  134  terminates with a stop member  156  which in turn is larger than the piston  134 . 
   The piston  134  rides in block  136  which includes an enlarged axial first cylindrical chamber  158  and a smaller aligned second cylindrical chamber  162 . First and second o-rings  164  and  166  are seated axially in chambers  158  and  162  respectively. Piston  134  is located in the first cylindrical chamber  158  and a seal is formed between piston  134  and the wall of chamber  158  by o-ring  164 . The shaft  148  of piston  134  extends through the smaller second chamber  162  and again forms a seal with o-ring  166 . The stop member  156  of piston  134  is larger than the large axial chamber  158  and acts as a stop limiting the movement of piston  134  relative to block  136 . 
   Block  136  further includes first and second threaded transverse openings,  168  and  172  respectively which lead to chamber  158 . The first threaded opening  168  is sealed by a bleed valve  174 . The second threaded opening  172  is connected to tube  54  which extends to pipe  16  which is downstream of pump  14  (Refer to  FIG. 1 ). Tube  176  further includes a strainer  178 . 
   The threaded end  152  of piston  134  attaches via turnbuckle  182  to throttle control linkage  184  which in turn is attached to the throttle  126 . 
   In operation when the engine  22  ( FIG. 1 ) is activated, it will cause pump  14  ( FIG. 1 ) to rotate increasing the water pressure in pipe  16 . ( FIG. 1 ) Tubing  54  and chamber  158  of block  136 . The water pressure (when it reaches a defined level) within block  136  will force the piston  134  to move to the left pulling the throttle back decreasing the rpm&#39;s for the engine and the output pressure from the pump. When the pressure is reduced below a defined pressure, the spring  144  will force the piston  134  back toward its starting position as shown in  FIG. 4 . The stop member  156  will engage a rear end of block  136  preventing further movement. When stop member  156  engages block  136 , the throttle  126  is positioned for the engine to provide its rated speed to drive pump  14  ( FIG. 1 ). 
   The present invention includes two mechanisms to adjust the operation of the control unit  128 . Between cap  142  and spring  144  are one or more metal disks or shims  192  which will increase the pressure applied by the spring against the piston  134 . By calculating the effect of a shim, one can determine the number of shims needed to achieve the necessary operating pressures. Alternatively, a bolt  194  could be threaded through cap  142  to adjust the pressure on spring  144  as best shown in  FIG. 4 . Further, turnbuckle  182  can adjust the position of throttle linkage  184  relative to shaft  152 . This will permit on site adjustment which may be necessary for engine  22  speed output to be trimmed to match pump  14  speed demand 
   The present invention provides an uncomplicated mechanism which accounts for increases in the pump pressure caused by changing flow rates, increases in pressure caused by engine droop as well as suction pressure. The simple pressure activated device of the present invention can be used to compensate for all of these automatically. The system itself does not require multiple adjustments for these three separate factors. This reduces the maximum pressure for a sprinkler system without limiting designed flow rate. Thus by utilizing the present invention, one can dramatically reduce the cost of a sprinkler system. 
   This has been a description of the present invention and the preferred mode of practicing the invention, however, the invention itself should only be defined by the appended claims.