Abstract:
An overpressure protection system provides for protection of a hydraulic system from elevated pressures. The system automatically stops flow to the system and prevents system pressure from exceeding a predetermined level. The system requires manual intervention to reopen flow, giving a worker the opportunity to resolve any system problems before system damage occurs.

Description:
PRIORITY 
       [0001]    The present application claims the benefit of U.S. Provisional Application Ser. No. 61/386,364, filed Sep. 24, 2010, which is herein incorporated by reference in its entirety. 
     
    
     THE FIELD OF THE INVENTION 
       [0002]    The present invention relates to a system for overpressure protection. More specifically, the present invention relates to an inline relief valve which prevents damage to hydraulic equipment due to overpressure of the hydraulic circuit. 
       BACKGROUND 
       [0003]    Hydraulic pressure is commonly used to power equipment such as generators, compressors, power tools, etc. Frequently, a power take off is used with a truck to provide power to hydraulic equipment. The power take off typically connects a hydraulic pump to a truck transmission. The hydraulic pump is connected to inflow and outflow lines that terminate in hydraulic quick release connectors at the back of the truck. 
         [0004]    Problems during use of the power take off and hydraulic equipment can damage the equipment. As an example, if the return line from the equipment to the pump is not properly connected, the return line remains closed and the hydraulic equipment experiences the full output pressure of the hydraulic pump as soon as the pump is engaged. Hydraulic equipment typically contains pressure sensitive components such as hydraulic fluid coolers on the return side of the hydraulic circuit. Subjecting these components to full hydraulic pressure will cause them to burst and will spill the hydraulic fluid as quickly as the truck hydraulic pump can pump the fluid. 
         [0005]    It is easily appreciated that it is desirable to protect the hydraulic equipment from overpressure situations in order to eliminate damage and to prevent hydraulic fluid spills. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present invention to provide an improved system for overpressure protection of hydraulic circuits such as hydraulic compressors, generators, or tools used with a truck power take off. 
         [0007]    According to one aspect of the invention, a compact overpressure protection valve is provided which closes the high pressure inflow line of a hydraulic circuit if pressure becomes too high in the low pressure side of the circuit. 
         [0008]    According to another aspect of the invention, a relief valve and catch tank is connected to the low pressure side of the system and to the overpressure protection valve to protect the low pressure components from high pressures. 
         [0009]    These and other aspects of the present invention are realized in an overpressure protection system as shown and described in the following figures and related description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Various embodiments of the present invention are shown and described in reference to the numbered drawings wherein: 
           [0011]      FIG. 1  shows a perspective view of a hydraulic system  10  incorporating the overpressure protection system of the present invention; 
           [0012]      FIG. 2  shows a perspective view of a part of the system of  FIG. 1 ; 
           [0013]      FIG. 3  shows a perspective view of the overpressure protection valve of  FIG. 1 ; 
           [0014]      FIG. 4  shows a schematic view of the overpressure protection valve of  FIG. 1 ; 
           [0015]      FIG. 5  shows a perspective view of the pressure relief valve of  FIG. 1 ; 
           [0016]      FIG. 6  shows a schematic view of the pressure relief valve of  FIG. 1 ; 
           [0017]      FIG. 7  shows a schematic view of the overpressure protection system of  FIG. 1 ; and 
           [0018]      FIG. 8  shows an alternate schematic view of the overpressure protection valve of  FIG. 1 . 
       
    
    
       [0019]    It will be appreciated that the drawings are illustrative and not limiting of the scope of the invention which is defined by the appended claims. The embodiments shown accomplish various aspects and objects of the invention. It is appreciated that it is not possible to clearly show each element and aspect of the invention in a single FIGURE, and as such, multiple figures are presented to separately illustrate the various details of the invention in greater clarity. Similarly, not every embodiment need accomplish all advantages of the present invention. 
       DETAILED DESCRIPTION 
       [0020]    The invention and accompanying drawings will now be discussed in reference to the numerals provided therein so as to enable one skilled in the art to practice the present invention. The drawings and descriptions are exemplary of various aspects of the invention and are not intended to narrow the scope of the appended claims. 
         [0021]    Turning now to  FIG. 1 , a perspective view of a hydraulically driven compressor using the overpressure protection device of the present invention is shown. Although a compressor is used as an exemplary device, the overpressure protection device may be used with many other types of hydraulic devices as well. The compressor, indicated generally at  10 , includes a hydraulic feed line  14  and return line  18 . The feed line  14  and return line  18  are connected to a hydraulic pump, such as a power take off of a vehicle. Hydraulic fluid passes from the power take off, through the feed line, through the compressor (or other hydraulically driven tool being used) and through the return line and back to the power take off. Before hydraulic fluid returns to the hydraulic pump through the hydraulic return line  18 , it passes through a fluid cooler  22 . The fluid cooler  22  is similar to a radiator, and cannot handle the full output pressure of the power take off pump. Problems occur when a return line is blocked or becomes clogged, pinched closed, or is not connected, for example. This causes the return line pressure to quickly rise to the full output pressure of the power take off pump, and causes the cooler  22  to burst, spilling hydraulic fluid. 
         [0022]    In order to prevent damage to the hydraulic system, an overpressure prevention valve assembly  26  of the present invention is attached to the high pressure inlet line  14 . The overpressure prevention valve  26  shuts off flow through the inlet line  14  if the pressure in a monitored low pressure line (a desired point in the system for protection from overpressure) exceeds a predetermined threshold pressure. A low pressure sense line  30  connects the overpressure protection valve  26  to the desired point of pressure protection in the system. 
         [0023]      FIG. 2  shows a partial perspective view of the back of the compressor  10 . A pressure relief valve  34  and overflow tank  38  of the present invention are provided to protect the cooler  22  from overpressure situations where return flow to the power take off is impeded or prevented and a pressure spike can not exit the system. The overflow tank  38  may be provided with a sight glass  42  or the like to allow a person to see the level of hydraulic fluid in the tank. 
         [0024]    If the return line  18  become blocked or restricted, such as where the line is crushed or a worker simply forgets to connect the return line  18  to the power take off system, the return line system demands. When the power take off is engaged, the pressure in the hydraulic system  10  will rise, often very rapidly. As soon as the pressure in the low pressure return side of the system  10  exceeds a selected pressure (often about 250 psi), the overpressure protection valve  26  closes flow from the power take off and, if necessary, the pressure relief valve  34  vents any remaining pressure in the low pressure side of the system  10  into the tank  38 . In order to restart the system, a person must usually manually relieve residual pressure in internal passages of the overpressure protection valve  26 . This prevents the power take off system from again providing pressure to the hydraulic system  10  before any issue is resolved, and reminds the worker to correct any problem in the system  10  before use. 
         [0025]      FIG. 3  shows a perspective view of the overpressure protection valve  26 . The overpressure protection valve  26  is connected to the high pressure hydraulic inlet  14  and a high pressure hydraulic outlet  46  which transmits the hydraulic fluid to the hydraulic system  10 . The overpressure protection valve  26  is also connected to the pressure sense line  30  and includes a valve handle  50  typically part of a manually operated poppet valve  74  to relieve pressure within the internal passages of the valve  26  as will be discussed below. 
         [0026]      FIG. 4  shows a schematic diagram of the internal components and passages of the overpressure protection valve  26 . The valve  26  uses a pilot-to-close check valve cartridge  54  such as a Sun Hydraulics COHA-XCN cartridge to connect the high pressure inlet  14  to the high pressure system line  46 . Hydraulic fluid flows through the inlet  14 , through the cartridge  54 , through internal passage  58 , and through hydraulic line  46  and to the hydraulic device  10  (i.e. the compressor or other machine operated by the pumped hydraulic fluid). The pilot-to-close valve cartridge  54  prevents back flow, and closes off flow when pressure in a pilot line  62  exceeds a predetermined pressure. A hydraulically-operated pilot valve cartridge  66 , such as a Sun Hydraulics DAAH-CAN valve cartridge, is connected to pressure sense line  30  through internal passage  70 . 
         [0027]    The sense line is a hydraulic line connecting the overpressure protection valve to a low pressure part of the hydraulic device  10  (such as to the hydraulic fluid cooler or another pressure sensitive component). When hydraulic pressure in the sense line  30  exceeds a predetermined threshold the pilot valve  66  opens and allows pressure to flow through the pilot line  62  and to the pilot inlet of the check valve  54 , closing the check valve  54 . Since overpressure in the system  10  is often caused by the failure to connect the return line  18  or by a clogged return line, closing the check valve  54  prevents a further rise in the system pressure, but does not relieve the system pressure. As such, the sense line  30  (and the hydraulic fluid within the protected device  10 ) remains at the pressure threshold which operates the protection valve and the check valve  54  remains closed. A manually operated poppet valve  74  is provided to allow a worker to relieve pressure in passage  62  via exit passage  78 . The vented hydraulic fluid may be contained in an overflow tank, or may simply be vented to the ground as it will typically be a negligible amount of fluid. Opening the relief valve  74  will lower the pressure in the pilot inlet of the check valve  54  and allow fluid to again flow through the check valve  54  and to the hydraulic device  10 . 
         [0028]      FIG. 8  shows a schematic diagram of the internal components and passages of an alternate configuration of the overpressure protection valve  26 . Similar to the configuration shown in  FIG. 4 , the valve  26  uses a pilot-to-close check valve cartridge  54  to connect the high pressure inlet  14  to the high pressure system line  46  via internal passage  58 . The pilot-to-close valve cartridge  54  prevents back flow, and closes off flow when pressure in a sense line  30  exceeds a predetermined pressure. A hydraulically-operated pilot valve cartridge  66  is connected to pressure sense line  30 . The sense line  30  is a hydraulic line connecting the overpressure protection valve to a low pressure part of the hydraulic device  10  (such as to the hydraulic fluid cooler or another pressure sensitive component). When hydraulic pressure in the sense line  30  exceeds a predetermined threshold the pilot valve  66  opens and allows pressure to flow through an internal pressure passage  72 , through the pilot valve  66 , through an internal pilot line  62  and to the pilot inlet of the check valve  54 , closing the check valve  54 . The internal pressure passage  72  is connected to the high pressure inlet  14  and the pilot valve  66  as shown. 
         [0029]    Since overpressure in the system  10  is often caused by the failure to connect the return line  18  or by a clogged return line, closing the check valve  54  prevents a further rise in the system pressure, but does not relieve the system pressure. As such, the sense line  30  (and the hydraulic fluid within the protected device  10 ) remains at the pressure threshold which operates the protection valve and the check valve  54  remains closed. A manually operated valve  74  such as a poppet valve is provided to allow a worker to relieve pressure in passage  62  via exit passage  78 . The vented hydraulic fluid may be contained in an overflow tank, or may simply be vented to the ground as it will typically be a negligible amount of fluid. Opening the relief valve  74  will lower the pressure in the pilot inlet of the check valve  54  and allow fluid to again flow through the check valve  54  and to the hydraulic device  10 . 
         [0030]      FIG. 5  shows a perspective view of the pressure relief valve  34  and overflow tank  38 . The pressure relief valve  34  is connected to a part of the hydraulic device  10  where pressure is to be monitored and overpressure prevented. This is typically a low pressure part of the system. A low pressure line  82  is connected to that part of the system, and the pressure relief valve  34  may be used to connect the sense line  30  to the low pressure line  82 . Alternatively, the sense line  30  may be separately connected to the part of the device  10  being monitored. 
         [0031]      FIG. 6  shows a schematic diagram of the pressure relief valve  34 . The valve uses a hydraulically-operated pilot valve  86  to allow flow from the system low pressure line  82  into the tank  38  via passage/line  90 . The pilot valve  86  may be selected to open at the same or a slightly higher pressure than the pilot valve  66 . The pilot valve  86  should not open at a lower pressure than pilot valve  66  as this would allow fluid to be vented into the overflow tank  38  (and likely overfilling the tank  38 ) without shutting off flow to the system  10  at the overpressure protection valve  26 . 
         [0032]      FIG. 7  shows a schematic diagram of the overpressure protection system including the overpressure protection valve  26  and the pressure relief valve  34 . In the case of overpressure of the low pressure line  82  (i.e. an overpressure in the part of the hydraulic device  10  to which the low pressure line is connected), the pilot valve  66  opens and stops flow through the check valve  54 . This happens almost instantly, preventing further pressure build in the device  10  and any sensitive system low pressure components. The pilot valve  86  typically opens to vent hydraulic fluid to the tank  38  and thereby lower the system pressure to below the predetermined protection pressure. Because hydraulic fluid has a low compressibility, typically about a teaspoon of hydraulic is vented to the tank  38 . Because closing pilot valve  66  does not relieve pressure in passage  62 , the check valve  54  remains closed. A worker must then manually open the poppet valve  74  to relieve passage  62  and open check valve  54 . Before doing so, the worker will preferably turn off the hydraulic source (i.e. the power take off) and determine why an overpressure situation has occurred. 
         [0033]    The present overpressure protection system is advantageous as it is simple and may be easily retrofitted to most hydraulically driven systems and equipment. It has been successful in preventing damage to low pressure hydraulic components and the resultant spills of hydraulic fluid. It is thus quite beneficial as it prevents system damage and down time, costly repairs, and the problems associated with large amounts of spilled hydraulic fluids. 
         [0034]    There is thus disclosed an improved overpressure protection system. It will be appreciated that numerous changes may be made to the present invention without departing from the scope of the claims.