Abstract:
A steam trap comprises a trap body having an inlet and an outlet each defining inner threads. The trap body further includes a spigot defining external threads. Also provided is a cap defining internal threads for engaging the external threads of the spigot of the trap body. A valve element freely moves inside a trap chamber defined between an inner surface of the cap and the valve seat of the spigot. The cap defines a top surface on which a disc of thermally insulative material is juxtaposed. A cup-shaped cover, which may carry indicia such as manufacturer name and model number, is received over the thermally insulative disc.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to steam traps used in steam distribution systems. More particularly, the invention relates to a steam trap adapted to control the escape of latent heat. 
   Steam traps, which are essentially automatic valves used to discharge condensate, are widely used in steam distribution systems. In operation, flash steam within the trap chamber of such devices functions to keep the valve closed. As the trap cools, the steam condenses and fluid pressure in the inlet passage forces the valve element off its seat. Condensate then passes through the trap, which eventually causes the valve element to again engage the seat. 
   The useful life of a steam trap is directly related to its cycle rate. Cycle rate is, in turn, related to latent heat loss. Accordingly, it is often desirable to control loss of such heat in a steam trap. While various configurations have been proposed to limit such heat loss, room exists in the art for novel constructions. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect, the present invention provides a steam trap comprising a trap body defining a seating face. A cap is fitted to the trap body and has a stop face. The trap body and the cap thus define a trap chamber. A thermally insulative element is juxtaposed to the cap. A valve element is located in the trap chamber and is displaceable between limit positions defined by the stop face and the seating face. 
   In some exemplary embodiments, the thermally insulative element substantially covers a top surface of the cap. Often, the thermally insulative element may comprise a disc of thermally insulative material such as a ceramic material. Preferably, the cap may define a wrenchable portion having a plurality of flats for engagement by a wrench. 
   Often, the cap may include a pin extending from the top surface thereof. In such embodiments, the insulative disc may define a central bore in which the pin is received. In addition, embodiments are contemplated in which a cover is received over the insulative disc. The cover may be attached to the pin so as to be securely maintained in position. In some embodiments, the cover may be configured having a top portion from which a circumferential skirt depends. 
   A further aspect of the present invention provides a steam trap comprising a trap body having an inlet and an outlet each defining inner threads. The trap body further includes a spigot defining external threads. Also provided is a cap defining internal threads for engaging the external threads of the spigot of the trap body. The cap defines a top surface on which a disc of thermally insulative material is juxtaposed. The disc substantially covers the top surface of the cap in this aspect of the invention. 
   Still further aspects of the present invention are achieved by an assembly for use with a steam trap body. The assembly comprises a cap defining internal threads for engaging external threads of a spigot of the steam trap body. The cap further defines a top surface on which a disc of ceramic material is juxtaposed. The disc substantially covers the top surface of the cap. A cover, configured having a top portion from which a circumferential skirt depends, is received over the insulative disc. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view of a steam trap constructed in accordance with the present invention; 
       FIG. 2  is cross-sectional view of the steam trap of  FIG. 1 ; 
       FIG. 3  is a view similar to  FIG. 1  with components of the cap separated for purposes of illustration; and 
       FIG. 4  is a cross-sectional view similar to  FIG. 2  but showing an alternative nameplate added to the top of the cap. 
   

   Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, such broader aspects being embodied in the exemplary constructions. 
     FIG. 1  illustrates a novel steam trap  10  constructed in accordance with the present invention. Steam trap  10  has a trap body  12  to which a cap assembly  14  is attached. Referring now also to  FIG. 2 , trap body  12  defines an inlet  16  and an outlet  18  through which the condensate flows. In this embodiment, inlet  16  and outlet  18  define internal threads for connection to a pipeline. 
   Inlet  16  is connected to an inlet passage  20 , whereas outlet  18  is connected to outlet passages  22 . Inlet passage  20  and outlet passage  22  emerge at a seating face  24  located at the end of a spigot  26 . As can be seen, cap assembly  14  includes a cap  28  having internal threads engaging outer threads on spigot  26 . 
   As can be seen most clearly in  FIG. 1 , cap  28  preferably defines a series of flats  30  about its periphery for engagement by a wrench. 
   Along with seating face  24 , cap  28  defines a trap chamber  32  in which a valve element in the form of a metal disc  34  is located. Disc  34  is movable upwardly and downwardly within chamber  32 , its movement being limited by seating face  24  and an opposed stop face  36  on the interior of cap  28 . Typically, body  12  and cap  28  are made from metal such as stainless steel. As a result, these components have a relatively high thermal conductivity. As noted above, latent heat loss from a steam trap causes the valve to cycle at a higher rate than otherwise desired. 
   In accordance with the present invention, it has been found that much of this heat loss occurs at the top surface  38  of the cap. Thus, a thermally insulated element, such as insulative disc  40 , may be juxtaposed to top surface  38  in order to substantially reduce the heat loss. In the illustrated embodiment, for example, disc  40  is configured to substantially cover the entirety of top surface  38 . Preferably, for example, disc  40  will have a diameter that just fits inside the hexagon of the cap to provide maximum coverage. 
   Although disc  40  may be made of any suitable insulative material (such as an insulating fiber with a low “R” value), it is often formed of a hard ceramic disc in presently preferred embodiments. In this regard, the disc may preferably have a thickness of ⅜ inch. While being more expensive than some alternatives, ceramic provides a very stable and uniform material with very consistent insulation properties. Any industrial grade ceramic is believed suitable, and it does not need to be alloyed with anything. 
   It is contemplated that disc  40  may be attached to top surface  38  of cap  28  by any suitable means. In the illustrated embodiment, however, cap  28  includes a vertical pin  42  which is received in a central bore  44  defined in disc  40 . Preferably, pin  42  and bore  44  are dimensioned to form a tight fit between these two components. As a result, disc  40  will be maintained securely in proximity to top surface  38  of cap  28 , without rotating. 
   In presently preferred embodiments, cap assembly  14  further includes a cover  46  fitted over insulative disc  40 . In this case, cover  46  is configured having a top portion  48  from which a circumferential skirt  50  integrally depends. As a result, cover  46  forms a cup shaped element in which insulative disc  40  is received. 
   Top portion  48  defines a hole  52  in which an end portion of pin  42  is received. Preferably, the length of pin  42  will be such that its end surface will be substantially flush with top portion  48  of cover  46  when the entire assembly is put together ( FIG. 2 ). Alternatively, hole  52  can be eliminated in which case the length of pin  42  will preferably be equal to the thickness of disc  40 . Either way, a small spot weld may be made between pin  42  and cover  46  to maintain it and disc  40  securely in position. 
   In presently preferred embodiments, cover  46  may be stamped from thin metal. For example, in some preferred embodiments, metal having a thickness of generally about 30 thousandths of an inch may be used for this purpose. Preferably, skirt  50  is dimensioned to leave a slight air gap  54  between it and top surface  38  of cap  28 . This has been found desirable to reduce thermal conduction which could cause cover  46  to undesirably function as a heat exchanger. 
   Advantageously, various indicia, such as manufacturer name, part number and the like, may be applied on the top portion  48  of cover  46  for both aesthetic and identification reasons. Alternatively, a separate plate  56  ( FIG. 4 ) with this information may be attached to the top portion of cover  46 . In this embodiment, plate  56  can be spot welded to pin  42  to maintain disc  40  and cover  46  in place. Although plate  56  is depicted with a diameter approximately equal to that of top portion  48 , embodiments are contemplated in which the diameter of plate  56  is either greater or less. 
   In operation, condensate reaches trap  10  at inlet  16 . The condensate flows through inlet passage  20 , lifting disc  34  off of seating face  24 . The condensate continues through outlet passages  22  and leaves trap  10  through outlet  18 . 
   As steam approaches the trap, the temperature of the condensate increases. When the hot condensate passes between disc  34  and seating face  24 , a portion of it evaporates and forms flash steam. The resulting expansion causes an increase in volume of the flowing mixture of flash steam and condensate, thus increasing the velocity. This causes a local reduction in pressure between disc  34  and seating face  24 , which pushes disc  34  into engagement with seating face  24 . 
   A steam bubble within chamber  32  retains disc  34  against seating face  24 , thus resisting the pressure in the upstream pipeline. It will be appreciated, however, that loss of latent heat will cause this steam bubble to collapse prematurely which results in excessive cycling of steam trap  10 . The presence of insulative disc  40  has been found to reduce the cycle rate by between 25% to 30%, which facilitates a possible increase in the useful life of the steam trap. In addition, disc  40  has been found to reduce the temperature of the condensate before discharge making steam  10  trap more energy efficient. 
   It can thus be seen that the present invention provides a steam trap having a novel configuration. While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of skill in the art without departing from the spirit and scope of the present invention. It should also be understood that aspects of those embodiments may be interchangeable in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only and is not intended to be limitative of the invention described herein.