Abstract:
A system and method of providing a high temperature hot water system assembly including a direct buried valve box that connects to one or more underground service pipes is disclosed. The buried valve box contains a valve assembly configured to control the flow of water through the one or more service pipes. An air gap within the valve box allows for movement and expansion of the components as the temperatures rise, preventing cracking or other failures. A bypass valve is also provided within the buried valve box, allowing for a small amount of hot water to flow through the service pipes to gradually increase the temperature. The direct buried valve boxes, controllable through valve risers that terminate in surface assembly boxes, eliminate the need for large, concrete underground vaults that make maintenance and operation of valve assemblies more difficult.

Description:
FIELD OF THE INVENTION 
     This invention pertains to valve assemblies for high-temperature hot water systems, and in particular to a pre-insulated and encased buried valve assembly operable using a surface valve access box. 
     BACKGROUND OF THE INVENTION 
     High-temperature hot water systems, which operate at temperatures typically exceeding 350° F. and pressures over 300 psi, are commonly used in large, hot water distribution systems. These systems may be, for example, district heating, which is a system used for distributing heat that is generated in a central location for residential, commercial, or government heating requirements. For example, university campuses, industrial manufacturing facilities, prisons, military or government bases or facilities, and may have district high-temperature hot water heating systems. As another example, they could be systems requiring high-temperature process applications including heat transmission for air and roller driers and washing equipment in kitchens, and sterilizers in hospitals or labs. 
     Currently, high-temperature hot water systems require the use of manholes, including large, underground concrete vaults that contain mechanical piping and valves exposed within the vault. To actuate these high-temperature valves, workers must remove the manhole covers and descend below ground into the vaults. However, workers are often reluctant to do so. These vaults are often confined spaces that are dark and hot, and require extra safety precautions and permits to enter and activate, close, adjust, and maintain the valves. These vaults can also be complex, with a plethora of different valves placed within the same area. This can make it difficult for workers to identify the high-temperature valve(s) that should be adjusted. 
     While buried valve assemblies have been used in some low-temperature water systems, these assemblies are not capable of handling high-temperature hot water. In particular, low-temperature buried valves cannot accommodate thermal expansion and do not allow drainage in the event ground water enters the system and comes in contact with the pipe, potentially causing flashing and system failure. They would therefore be incapable of use in a high temperature environment. Thus, what is needed is a direct buried valve, with surface access boxes to activate and control the valves, allow drainage, which can be used in high temperature water systems. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system and method for a direct buried valve for a high-temperature hot water system. The direct buried valve is buried in the ground, instead of being placed within an underground vault. The valve assembly may be a pre-insulated and encased valve, such as a butt-welded ball valve. A watertight enclosure may encase the valve, and a bypass warm-up valve may also be included within the enclosure. The enclosure may contain a support for the valve including a steel plate, an outer steel casing, insulation, an air gap allowing for expansion of the outer casing and other steel components in the system, and a jacket. The jacket may be a fiber-reinforced polymer (FRP) jacket, or a high density polyethelyne (HDPE) jacket. A short segment of pipe extending from each side of the valve and a steel anchor plate can be provided as a part of the assembly to ease installation and ensure that the full assembly remains watertight. The anchor plate minimizes movement at the valve location. The system may then expand towards expansion loops or expansion joints elsewhere in the system. Steel guides are provided around the service pipe inside the outer casing assembly just outside of the valve box to allow for the service pipe to remain supported while providing directional guidance for it to thermally expand. A valve stem riser may be connected into the enclosure and extend to a surface valve access box located near surface grade. If a bypass valve is included, a bypass valve riser stem may also be connected to the enclosure and extend to the surface valve access box. Controls within the surface valve access box allow an operator to open, close, and adjust the buried valves near surface grade. 
     Although the enclosure for the buried valve is configured to be watertight, it is possible that seals or gaskets may fail, or that the outer jacket may become compromised. In such situations, it is possible that water could enter the enclosure. In order to avoid damage to the valves caused by water in the enclosure, a drain may be provided to allow the system to drain any water from the enclosure before it turns to steam, which could cause rapid deterioration or an explosion or otherwise damage the buried valves, risers, and piping. Alternatively, the outer casing can be installed in a manner to allow the system to drain from the valve box to the pipe&#39;s air space and out to a low point drain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a buried valve box. 
         FIG. 2  is a side view of a buried valve box. 
         FIG. 3  is a view of a valve stem riser and surface access box. 
         FIG. 4  is an illustration of the buried valve box, water pipes, and stem risers. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The system and method are directed to a direct buried valve assembly for use in high-temperature hot water systems. The system includes a buried valve assembly, valve stem risers, and a surface valve access box. 
     As shown in  FIG. 1 , which illustrates a top view, the buried valve assembly includes valve box  100 , which is connected to one or more outer conduits  105 . Service pipes  101  enter the interior of the buried valve box  100 , where they join valve assembly  102 . The services pipes  101  are used for distributing the high-temperature hot water from a district plant to buildings the system serves. The service pipe and valves are fully isolated from the outer casing/insulation/jacket, allowing the system to float inside the air space except at the anchor locations. Valves are provided prior to entering each building so that the system can be operated to allow for isolation of the system for maintenance. In the event the system needs to be worked on the valves can be closed to prevent high temperature hot water from entering the line being worked on but can remain operational to other areas connected to the system. Typically three valves are installed at each branch for both the supply and return piping. 
     The valve box  100  may be formed as a watertight container using an outer casing, such as steel, with insulation  104  and a watertight jacket  103 , having an open interior area. The outer casing of the valve box  100  may join with or be integral with an outer conduit  105  surrounding connected service pipes  101 . For example, a section of a service pipe may be included on either side of the valve box, as part of the overall assembly. This allows for easy connection to service pipes in the area of the buried valve box, while helping to ensure that the enclosure remains water tight by minimizing field joints. The outer conduit may be formed of steel, and may be at least 0.25 inches thick. The valve box may be encased in an outer insulation material  104 , surrounded by an outer jacket material  103 . The thickness of the outer jacket may vary, and the jacket may be formed from various materials. For example, the jacket  103  may be a 250 mm thick extrusion welded HDPE jacket, or a 125 mm thick FRP coating. Preferably, the outer insulation material  104  is positioned in the space between jacket  103  and the outer conduit  105 . 
     As seen in  FIG. 1 , interior insulation  108  is provided adjacent to the service pipes  101 , with an air gap  106  formed between the service pipes  101  and the outer conduit  105 . A guide  107  may be included to help provide support while maintaining the separation of the pipe  101  from the outer conduit  105 , ensuring that the air gap  106  remains open. The air gap allows for thermal expansion and movement of the service pipes  101 , which often occurs in high temperature water systems and also allows for system draining in the event water enters the space. 
     The interior of valve box  100  is mostly open, again allowing for thermal expansion and movement of the components contained therein. Valve assembly  102  may be located in the center of the valve box  100 . Valve assembly  102  is connected to pipes  101 , allowing for adjustment of the water flow therein. When valve assembly  102  is closed, it stops the flow of water through the pipes. Valve assembly  102  may be opened to allow water to flow, and the extent to which the valve is opened may be adjusted to control the flow of water. Valve assembly  102  may be a class  600 , triple-offset, butt-welded, high-performance butterfly valve. Other types and classes of valves may also be used, such as gate valves or class  300  valves. Prior to installation, the valves  102  may be hydrostatically and leak tested. 
     In addition to valve assembly  102 , a bypass valve assembly  110 , including a valve and lines connecting into service pipes  101 , may be provided. The bypass valve assembly  110  allows for a small amount of water to flow through the pipes  101 . This allows an operator to slowly warm up the system, so that it can expand at a reasonable rate, avoiding failure and cracking of the pipes, valves, or other components. Without a bypass valve  110 , if valve assembly  102  was opened and a full amount of hot water allowed to run through the valves, pipes, and other components before they were sufficiently warmed, the valves, pipes, or other components could crack or burst. Implementation of the bypass valve  110  allows an operator to control the rate at which the temperature of the system increases, thereby avoiding sudden increases that could stress or crack system piping or other components. 
     In addition, a valve insulation material  111  may be provided around the valve assembly  102  and bypass valve assembly  110 , including the bypass valve and bypass lines. This valve insulation material may be, for example, a silica aerogel, cellular foam glass, mineral wool, calcium silicate, or other insulating materials. A support plate  109  and service pipe saddle supports  112  may also be included in the interior of the valve box  100 . These supports help to support the weight of the service pipes  101  and valves  102 ,  110  within the open interior of valve box  100 , and further serve to maintain the proper positioning of the pipes and other system components. A drain pipe  113  extends from a flange  114 , which may be welded to the outer conduit  105  of the valve box. The drain pipe allows for any water that may build up in, or leak into, the valve box to drain away before it can change to steam under the high temperature conditions and cause damage. Without such a drain pipe, any water present in the interior of the valve box may become heated and turn to steam, potentially causing an explosion of the valve box or damage to the pipes, valves, or other components in the box. Alternatively, the outer steel conduit  105  can be oversized near the valve box  100  and positioned so the bottom of each align allowing for the system to drain thru the outer steel conduit  105  to a low point drain assembly in the system. A check valve may be installed with the drain pipe, preventing water entering the valve box through the drain pipe. The drain pipe may be installed to a standard storm or sanitary sewer drainage structure and discharged into the storm or sanitary sewer system. 
       FIG. 2  illustrates the direct buried valve box from a side view perspective. As can be seen, the drain pipe  113  extends from the bottom of the valve box  100 , allowing water exit the valve box. The drain pipe  113  may drain into a drain vault located at a predetermined distance from the valve box  100 . Alternatively, the drain pipe  113  may drain into a larger drain pipe, another piping system, or directly into the surrounding earth. The valve box also contains a valve stem riser  115  and riser conduit  116 , extending from valve box  100  to surface grade. The valve stem riser  115  may be encased within an insulated riser conduit  116 . The valve stem riser  115  and riser conduit  116  may be formed similar to the piping  101 . For example, the valve stem riser  115  may be provided within a casing, with air or insulation material filling the space between the riser  115  and casing. In addition, another layer of insulation may surround the outside of the casing, and this insulation may be covered by an outer jacket. The valve stem riser allows for control of the valve from the surface, rather than requiring a manhole and complex, underground vault that an operator must enter. The riser conduit  116  is a steel conduit that is attached to the valve box, for example by welding. Insulation and jacket similar to the valve box can be provided. The riser conduit houses the valve stem/shaft. The valve stem extends from the valve gear operator towards the valve box assembly above. A tee wrench that has a socket fitting the valve operating nut may be provided by the valve manufacturer. Operators can remove a flange located below the access cover  303  and use the wrench to open and close the valve. 
     In the system, the outer insulation keeps the internal temperature contained to prevent grass, trees, or other landscaping above the buried valve assembly from being affected by the heat of the high temperature hot water. The insulation thickness and materials may be selected based on the depth of the valve box, and the amount of heat within the system. The insulation thickness may be further selected so that the air gap between the insulation and the outer conduit does not cool to a temperature where condensation may occur. The outer jacket of the system is desired to keep the entire assembly watertight and prevent water intrusion into the system. Similarly, the insulation materials provided within the interior of the outer conduit are designed to maintain a high enough temperature that condensation does not occur, while keeping the system cool enough that the outer conduit or jacket would be stressed or rupture. The ideal air gap temperature is between 180° F. and 212° F. 
       FIG. 3  provides an illustration of the valve stem riser conduit  116  close to the surface. As shown, the riser conduit  116  containing the valve stem riser may be brought close to the surface, where it terminates within an enclosed space under a removable cover  303 , such as an easily-removable cover similar to a manhole cover. For example, the valve stem riser may be brought to around 18 inches from the surface and sealed with a bolted flange, where it terminates in surface valve access box  300  under the removable cover. The valve access box  300  may be a precast concrete ring with a gravel base that protects the riser from water intrusion while maintaining access. The top of the valve stem riser may include a control  301 , allowing an operator to open, close, or adjust valve  102  located in the buried valve box  100  by using a tee wrench fitted with a socket fitting the valve operating nut. The enclosed space may be formed using a concrete collar  302  which surrounds the top of the valve stem riser  115  and riser conduit  116 . When a bypass valve assembly is included in the valve box, a bypass valve stem riser and shaft may also be included. 
       FIG. 4  provides an illustration of a high-temperature hot water buried valve system. The buried valve box  400  is connected to outer conduit pipes  401 , and has a drain pipe  411  extending from a flange  410  in the bottom of the valve box  400 . Main valve  402  and bypass valve assembly, including bypass valve  403 A and bypass lines  403 B, are included within the interior of the buried valve box  400 . A valve stem riser  404  extends from main valve  402  toward the surface, terminating at a valve control  408 . Valve stem riser  404  is contained within shaft  406 . Similarly, the system includes a bypass valve stem riser  405  contained within shaft  407  and terminating at bypass valve control  409 . Valve stem riser  404  and bypass valve stem riser  405  may terminate in one or more surface valve access boxes. An operator may open the surface valve access box, and use removable controls  408  and  409  to adjust main valve  402  or bypass valve  403 A. To open, close, or adjust the main valve, an operator would access the surface valve access box, and use control  408  to open or close valve  402  a desired amount. 
     As mentioned, if the system has not been in use, such that the components and piping have cooled, it may be beneficial to first control the bypass valve  403 A and allow the system to slowly warm. To do this, an operator may access the surface valve access box, and adjust the control  409 . By adjusting the control, the operator can open the bypass valve  403 A at a desired rate, thus allowing a controlled amount of high temperature hot water to flow through bypass lines  403 B within the valve box  400  and into the service pipes  401 . By allowing the controlled amount of water to flow through bypass lines  403 B, the operator can slowly raise the temperature of the high temperature hot water buried valve system. This allows the system components to expand at a reasonable rate, avoiding cracking or failure that could occur if sudden temperature changes were introduced by first opening the main valve and allowing the full amount of hot water to flow through the system. As also mentioned, the various air gaps provided within the system, as well as the positioning of the insulation materials, allow the pipes, valves, and other components to expand and contract within the system. This allowance for movement enables the system to handle the high temperature hot water without cracking or failure. 
     Providing drain pipe  411  provides an additional prevention against failures in the system. By providing the drain, any condensation that builds up in the system and any external water that makes its way into the system can be safely removed before becoming heated to steam. If no drain were provided, water that either leaked into the system through a compromised area, or condensation that significantly built up within the system, could turn to steam and cause greatly increased pressures. These increased pressures may be too extensive for the system components to handle, and pipes, valves, or other components could crack, rupture, or explode. 
     In addition to being used in an underground, buried valve assembly, the system described above may also be implemented in an above ground system where double containment is preferred. Above ground double containment may be preferred in locations that have above ground high temperature piping that is near occupied spaces such as near buildings on military bases or in prison yards. If a system can become compromised due to impact, having double containment around the pipe makes it more difficult for the system to be damaged. Similarly, if there was a rupture on the service pipe, the outer casing could contain the steam that would be released from said rupture. The steam would then be released at a controlled air release point installed in the system.