Bimetallic controlled steam trap

A steam trap has a bimetallic control element provided on the prepressure side and a locking part which is biased by the prepressure in the opening direction and which is actuated by the bimetallic control element. The bimetallic control element is provided with at least one bimetallic snap disk and the valve seat is stroke-movably positioned, whereby the maximum stroke path of the valve seat is only a part of the operating stroke of the locking part.

The present invention relates to a steam trap. More particularly, it 
relates to a steam trap having a bimetallic control element provided on 
the prepressure side and a locking part which is biased in the opening 
direction by the prepressure and which is actuated by the bimetallic 
control element. 
In such a steam trap, an intermittent manner of operation is desirable, 
i.e., an abrupt wide opening and also an abrupt complete closing. For this 
purpose, it is known, for example, to provide a large pressure admitting 
face downstream from the locking or closing part, so that the outflowing 
condensate exerts an additional opening force on the locking part and 
thereby may effect a further wide opening. However, this additional 
opening force is created only after a certain opening stroke of the 
locking part has been effected, i.e., after the flow of condensate has 
already begun. 
Therefore, with small quantities of existing condensate, a balance 
situation is generated in this stroke area between the closing or locking 
forces of the bimetallic control element and the opening forces on the 
closing or locking part generated by the pressure. The locking part, in 
this case, remains in this throttle position and does not snap into the 
wide-open position. The consequence is that a high degree of wear and 
interfering polluting sediments deposit on the sealing faces of the 
locking part and the valve seat. 
It is therefore an object of the invention to provide a steam trap of the 
aforementioned type, the locking part of which snaps to a wide open 
position from the locking position in a rapid manner, even when only small 
amounts of condensate are present and which again rapidly closes after the 
condensate is discharged. 
This object of the invention is achieved by the provision of a steam trap 
of the aforementioned type wherein the bimetallic control element is 
provided with at least one bimetallic snap disk and the valve seat is 
stroke-movably positioned so that the maximum stroke path of the valve 
seat is only a portion of the operating stroke of the locking part. 
Generally, bimetallic snap disks run through their stroke in essentially a 
jump-like manner. Therefore, they are suitable, per se, to effect an 
intermittent operation of the steam trap without a pressure admitting face 
downstream from the locking part. However, it had been found that the snap 
movement does not occur from the full locking force, i.e., from the end 
position of the locking part, so intermediate throttle opening positions 
may occur when only small amounts of condensate are present. In accordance 
with the invention, the stroke movable valve seat follows the locking part 
in the first critical stroke phase and therefore assures a reliable 
closing or locking. The locking force is the result of the available 
pressure load on the valve seat. During the first stroke phase, the 
bimetallic snap disk reaches a point where it completely snaps through to 
the other end position, with the stroke movement of the valve seat ending 
prior thereto. 
During the closing or locking procedure, the locking part is snapped 
against the valve seat by the bimetallic snap disk, thus generating an 
immediate reliable closing or locking. During the remainder of the slow 
stroke movement of the bimetallic snap disk, the locking part is then 
lifted together with the sealingly-engaged valve seat. Therefore, 
disadvantageous intermediate throttle openings are always reliably 
prevented. 
Other objects and features of the present invention will become apparent 
from the following detailed description when taken in connection with the 
accompanying drawing which discloses one embodiment of the invention. It 
is to be understood that the drawing is designed for the purpose of 
illustration only, and is not intended as a definition of the limits of 
the invention.

Turning now in detail to the drawing, there is shown a separating wall 1 
between the prepressure or high pressure side and the low pressure side of 
a steam trap housing (not shown) having a lead aperture 2 for the 
condensate to be discharged. A control unit 3 is mounted on wall 1 for 
controlling the flow through lead aperture 2. 
Control unit 3 is provided with a base portion 4 having a central opening 5 
and supports 6 for a bimetallic snap disk 7 provided on the prepressure 
side. Snap disk 7 actuates a locking part 8 which is biased in the opening 
direction by the prepressure and which cooperates with a valve seat 9. 
Valve seat 9 is provided on a stroke-movable annular element 12 which is 
disposed or limited movement between two stroke abutments 10 and 11. An 
annular membrane 13 is coupled in a pressure-tight manner with annular 
element 12 and base portion 4 by means of its inner and outer edges, 
respectively, thus preventing the medium from flowing laterally around 
annular element 12. 
If steam is present on the prepressure side, then the bimetallic snap disk 
7 is convexly upwardly arched and it retains the locking part 8 with a 
high degree of locking force against the valve seat 9. Thereby, annular 
element 12 is supported against stroke abutment 10 (FIG. 1). Consequently, 
steam cannot escape into lead aperture 2. 
As soon as bimetallic snap disk 7 is exposed to the condensate, the closing 
force of bimetallic disk 7 decreases due to the lower temperature and 
bimetallic snap disk 7, together with locking portion 8, initially 
executes a gradual slow stroke. The strok-movable annular element 12 
follows locking part 8 under the action of the prepressure, so that in 
this phase, locking part 8 and valve seat 9 are still sealingly engaged 
(FIG. 2). Thereby, the effective locking force is defined by the 
pressure-admitted face of the annular element 12 and the pressure 
difference or differential pressure between the prepressure and the low 
pressure sides. In the meantime, bimetallic snap disk 7 reaches the state 
wherein it abruptly moves the remainder of the stroke path, thus rapidly 
moving locking part 8 into the opening position. 
At the same time, annular element 12 is prevented from a further stroke 
movement by stroke abutment 11 (FIG. 3). Therefore, the steam trap always 
opens from the secure closing position into the wide open position. 
When bimetallic disk 7 is again heated to its locking temperature, after 
the discharge of the condensate, due to its exposure to the steam once 
again, it snaps from its concave configuration (FIG. 3) into its covex 
configuration (FIG. 2). As a result, locking part 8 comes into engagement 
with valve seat 9 and raises annular element 12 from stroke abutment 11. 
In this manner, a tight sealing is obtained at the sealing location 8,9. 
When bimetallic snap disk 7 slowly moves through the remainder of the 
stroke, the steam trap is already closed. 
Disadvantageous intermediate throttle opening positions as they may occur 
during the presence of low amounts of condensate and constant opening and 
closing strokes of the locking part 8 are thereby reliably prevented in 
this manner. Despite the amount of condensate present, the steam trap 
exclusively operates in an intermittent manner, i.e., it always opens from 
the secure closing position into a wide open position and again completely 
closes from such a wide open position. 
Thus, while only one embodiment of the present invention has been shown and 
described, it will be obvious that many changes and modifications may be 
made thereunto, without departing from the spirit and scope of the 
invention.