Abstract:
An emergency tempered water blending apparatus is described which has a threeway, thermostatic mixing valve for mixing a cold water intake stream with a hot water intake stream at effective proportions to form a tempered water output stream having a desired, preset temperature. When the flow of the cold water is detected, a normally-closed valve in the tempered water stream opens allowing flow to the user. Water flow defaults to cold water upon either a mechanical or electrical failure, or upon the temperature of the tempered water becoming too hot to reduce probability of failure in hot mode.

Description:
This application is a continuation of application Ser. No. 09/386,502, filed Aug. 30, 1999, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to tempered water blending systems particularly useful on emergency safety showers. 
     BACKGROUND OF THE INVENTION 
     Tempered water safety showers are used in a wide range of industries in which workers are exposed to toxic and hazardous chemicals that can cause serious tissue damage upon contact. Occupational Safety and Health Administration regulations require the availability of emergency safety showers for use as a form of first aid treatment. ANSI standard Z358.1 requires that these showers can deliver at least 20 gallons of water per minute for a time period of 15 minutes over the body of a person who has been exposed to an aggressive chemical. 
     It has been found that there are problems relating to a 15-minute sustained time in cold water for any individual, and particularly for a person who is already in or subject to traumatic shock. The body quickly begins to react to the cold by shivering in order to fight off cold and generate body heat. The sustained flow of cold water increases the loss of body heat beyond the body&#39;s ability to maintain adequate temperature levels and further stimulates the metabolic rate to compensate. Ultimately, the user enters thermal shock and/or refuses to remain in the shower for the time required for adequate treatment. Moreover, use of cold water discourages the effective, maximum use of the safety shower temperature for the 15-minute period which is required by the ANSI standard. Users tend to leave the shower much earlier when being deluged with cold water. 
     Tempered water blending systems usually provide drench water at almost 85° F-90° F., and at the temperature levels sufficient to provide relief to the affected tissue while allowing the user to remain immersed for the required treatment period. Most systems use basically mechanical, temperature-control devices which respond sluggishly to temperature changes with a pressure drop across the system of from about 30 to 40 psi. Even later-model electro-mechanical systems that allow existing plant hot and cold water supplies to be accurately and safely blended to a preset, non-adjustable, safe, utilization temperature leave something to be desired as far as responsiveness and fail-safe operation is concerned. Such systems are readily available in industrial safety catalogs. Because of this and other desires for tempered water safety showers, there exists a need for the development of a tempered water emergency shower that is simpler, more economical and safer to use. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a simple, economical and safe emergency shower apparatus for supplying tempered water having a desired, pre-selected temperature within a fraction of the time required using existing systems. The apparatus of the present invention provides a steady flow of tempered water having a preset temperature without significant temperature fluctuation. Temperature fluctuation is less than about ±3° F. The present invention accomplishes the desired outlet water temperature within a period of time less than about 1 second of the manual opening of a flow valve such as a safety shower head. The time it takes for the establishment of a steady flow of tempered water flow having the desired preset temperature from the sensing of flow after opening the flow control valve by the user is referred hereinafter as the response time. In contrast, current systems generally take much longer to establish a steady water flow having the desired preset temperature. 
     It is an object of the present invention to provide a tempered water shower apparatus having an infinitesimal probability to fail in hot mode, thereby providing a much safer device than prior art devices. For instance, the present invention apparatus is designed to fail (if such should occur) in the safe, not hot, mode. 
     These and other objects of the present invention will become apparent to an engineer with ordinary skill in the art of emergency tempered water safety systems from the following discussion. In accomplishing these objects, an apparatus is provided for supplying tempered watercomprising a three-way, thermostatic, self-operated mixing valve for mixing the flow of a cold water stream with a hot water stream at effective proportions to form an output water stream having a temperature of a desired, preset temperature. The apparatus employs a sensor which detects the flow of the cold water stream to cause a normally closed solenoid valve in the tempered water line to open. The system includes a controller programmed to close the tempered water flow upon either a mechanical or electrical failure, or upon the temperature of the tempered water reaching a temperature greater than a predetermined value, while allowing flow to continue through the cold water bypass which is designed to flow about 30 gpm. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The drawing shows a flow diagram showing a preferred embodiment of the present invention tempered water apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing, there is shown the preferred embodiment of the tempered water system  10  of the present invention, having a cold water supply line  12 , a hot water supply line  16  and a three-way self-regulating thermostatic mixing valve  18 . Thermostatic valves are generally well known, e.g., as shown in U.S. Pat. Nos. 4,739,793; 4,767,052; and 5,647,531 which are incorporated by reference herein for all purposes. The preferred valve is an AMOT® valve Model C manufactured by AMOT Controls (Richmond, Calif.). These valves are well known to those skilled in the art. 
     Generally, the mixing valve  18  of the type used in the present invention comprises a valve body having cold-water inlet  18   a , hot-water inlet  18   b , and a tempered water outlet  18   c . The cold-water inlet  18   a  and hot-water inlet  18   b  are connectable to pressurized cold and hot-water intake lines  12  and  16 , respectively. The intake lines  12  and  16  are connected to plant supply lines. The valve body  18  defines a chamber having cold- and hot-water compartments connected to the cold- and hot-water inlets  18   a  and  18   b , respectively, and to a mixed, tempered water compartment connected to the outlet  18   c . Cold- and hot-water seats within the mixing valve  18  are bounding the respective inlet compartments. The valve  18  further comprises a thermostatically controlled actuator disposed within the mixed, tempered water compartment. The actuator is operatively connected with a valve closing body via a valve stem. 
     The valve closing body is displaceable between one end position engaging the hot-water seat, blocking flow from the hot-water inlet and permitting flow from the cold-water inlet and on opposite end position engaging the cold-water seat, blocking flow from the cold-water inlet and permitting flow from the hot-water inlet. In intermediate positions flow from both cold- and hot-water inlets is permitted through the mixing valve  18  into the tempered water outlet  18   c . In the present invention this proporting valve is preferably initially set to allow flow of about 87 percent cold and 13 percent hot water. The temperature of the entering water streams and the desired outflow stream will determine the ultimate operating properties which, of course, are subject to change under actual operation. 
     The thermostatic actuator, or proportioning valve, in mixing valve  18  is capable of changing position or shape dependent upon temperature and can act on the valve closing body to move it to keep the temperature of the water in the outlet chamber substantially constant to a preset temperature. It is understood, of course, that many different types of self-regulating, thermostatic, mixing valves could be used in the practice of the present invention which are well known to the skilled process control engineer. The preferred mixing valve will have a flow coefficient of from about 7 to about 12, preferably of from about 8 to about 11, and most preferably of from about 9 to about 10. The pressure drop across the three-way mixing valve at a flow of 30 gallons of water per minute is from about 4 to about 12 psig, preferably from about 7 to about 8 psig. 
     According to the preferred embodiment of the present invention, a check valve  40  is operatively positioned in the cold water intake line  12  between the three-way mixing valve  18  and a flow sensor  14 . The check valve  40  is selected to prevent flow or migration of hot water into the cold water line  12  during long periods of non-use or stand-by duty. Preferably, a check valve having a flow coefficient of from about 20 to about 40 should be used. The pressure drop across the check valve at a flow of about 26 gallons of water per minute should be from about 0.2 to about 1.1 psig, preferably from about 0.4 to about 0.9 psig. Of course, it is understood that many different types of check valves could be used without departing from the scope of the present invention. 
     An outlet line  20  is connected to the outlet  18   c  of the three-way, mixing valve  18 . Outlet line  20  has a first normally-closed solenoid valve  22 , and a temperature sensor  24  disposed downstream of the first normally-closed solenoid valve  22 . A controller  32  is operatively connected to the sensor  24 , the first normally-closed solenoid valve  22  and flow switch  14  through lines  34  and  36 , respectively. 
     A cold water bypass line  42  connects to the cold water inlet line  12  at a joint  26  downstream the flow switch  14  and to the outlet line  20  at a point  28  downstream the first normally-closed solenoid valve  22 , bypassing the mixing valve  18 , and upstream of the temperature sensor  24 . Bypass line  42  has a second normally-open solenoid valve  30  operatively positioned therein and operatively connected to the controller  32  through connector  38 . It should be understood that any type of operative connections can be used to establish communication between the controller  32  and the temperature sensor  24 , first and second solenoid valves  22 ,  30  and flow sensor  14 . For instance, infrared, radio or other communication means could be used in addition to electrical or optical hard connections. The bypass line  42  intersects the outlet line  20  at  28  downstream of the first normally-closed solenoid valve  22  and at a position where the temperature sensor  24  can determine the tempered water temperature. Normally the intersection  28  will be upstream of temperature sensor  24 , but for purposes of this system, placing the temperature sensor  24  at the intersection  28  will be considered to be upstream of the sensor  24 . 
     In operation, when the user opens a valve of a safety shower head (not shown), flow begins in cold water line  12 , and flow sensor  14  transmits a signal to controller  32  and to first normally-closed solenoid valve  22  which opens. At the same time second normally-open solenoid valve  30  in the cold water bypass  42  is caused to close by either the direct  26  signal from the flow sensor  14  or controller  32 . Within seconds tempered water having a preset desired temperature, normally from about 85°-90° F., will flow through line  20 , past thermostat  24 , and out the shower head  46  to drench the body of the user. Depending upon the size of the maximum flow rate chosen, the flow rate is from about 3 to about 30 gallons per minute (3 to 60 gallons per minute on higher volume systems), preferably of from about 25 to about 35 gallons per minute, and most preferably, in the system of the present invention, at about 30 gallons per minute. Cold and hot water enter mixing valve  18  through lines  12  and  16 , respectively, at volumetric rates dependent upon the preset desired temperature of the tempered water. Preferably the mixing valve is set to allow the initial outlet flow to have about 13 percent hot and 87 percent cold water. This, of course, will vary with the temperature of water sources available. Tempered water exits outlet  18   c  of the mixing valve  18  through outlet line  20 , first normally-closed solenoid valve  22  and temperature sensor  24 , and through a shower head or eyewash assembly. The system design, to on a safety shower, can be sized to provide up to 60 gallons of water per minute, preferably up to 30 gallons of water per minute at the desired preset temperature. Since it is normally connected to a plant water supply, it will operate almost indefinitely. The temperature may be preset to any temperature between from about 50° F. to about 95° F., preferably from about 80° F. to about 90° F. 
     The preferred embodiment as shown in the drawing requires a minimum of 40 psi inlet pressure, maximum 80 psi inlet pressure, and maximum 10 psi differential pressure between the hot- and cold-water inlet streams. It operates over wide water supply temperature ranges to achieve 85° F. outlet temperature with maximum cold inlet temperature ranging from about 30° F. to about 82° F. In the event of electrical or mechanical failure, the first normally-closed solenoid valve  22  will close and the second normally-open solenoid valve  30  will open to put the apparatus in cold water by-pass mode with the system supplying cold water only through outlet line  24 . Even with no electrical power available, cold water will flow, hot water will not, and the system of this invention will, even though uncomfortable, accomplish the drench function under an electric power outage. Thus, in the event of breakdown or disaster, as long as there is water available to the system, the system will function to deliver water to the shower. 
     The components of the apparatus of this system are minimized and are selected to reduce the overall pressure drop experienced in prior art systems. Therefore, the selection of components are to be considered. First normally-closed solenoid valve  22  and second normally-open solenoid valve  30  have flow coefficients of from about 8 to about 16, preferably from about 9 to about 15. The pressure drop across the solenoid valves  22  and  30  should range from about 3 to about 9 psig, preferably from about 5 to about 7 psig, at a flow of about 30 gallons of water per minute. Of course, it is understood that any of many different types of solenoids which are well known to the skilled process engineer can also be used. The primary consideration is the selection and installation of the solenoid valves in that the one in the cold water bypass valve defaults to the open position and the hot defaults to the closed position. 
     Flow sensor  14  is a readily available device selected to have a flow coefficient of from about 8 to about 10. The pressure drop across flow switch valve  14  should be from about 5 to about 11 psig at about 26 gallons of water per minute. Of course, it should be understood that many different flow sensors could be used without departing from the scope of the present invention. 
     Controller  32  is connected to the flow sensor, solenoid valves and temperature sensor, and may be fabricated from a number of relays, solid state circuitry or a computer with software. Such a device is well within the skill of the ordinary control engineer. The controller was tested in a number of situations relating to the failure of the mixing valve and thermostats, temperature sensing devices, such that an attempt was made to cause the system of this invention to fail in an unsafe mode; i.e., where hot water would exit the system. 
     The blending system of the present invention is designed to have a minimum probability to fail in hot mode, thereby providing a much safer device than previously available. It is adaptable to any device providing a tempered water flow, particularly safety shower or eye wash fountains, and can be retrofitted into existing operational systems. 
     It should be understood that the above description of the preferred embodiment is given by way of illustration for complying with the statutory requirements of enablement and best mode of patent law. Nothing in the above description should be construed as limiting the scope of the invention as this scope is defined in the appended claims, and changes in the system may become readily apparent to those skilled in the art without departing from the invention described and claimed herein.