Note: Descriptions are shown in the official language in which they were submitted.
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STEAM TRAPS
This invention xelates to steam traps.
The invention is particularly concerned with
thermostatic steam traps having a so-called "balanced
pressure" thermostatic element which in one type of trap
takes the form of a sealed bellows with a rigid metal
top and bottom, but with a side wall wh`ich will lengthen
or shorten if the rigid ends are pulled apart or pushed
together. The rigid top is fast with the body of the
trap whilst the rigid bottom carries the valve member
of the trap. The bellows is filled with a volatile fluid.
In operation this fluid is heated by condensate present
in the trap such that at a condensate temperature at
or above a predetermined temperature t below the saturated
steam temperature corresponding to the pressure at the
trap, the bellows ls sufficiently expanded for the valve
member to be seated on its seat to close the trap. At
condensate temperatures below t the bellows is collapsed
and the trap is open.
An aspect of the invention is as follows:
A thermostatic steam trap comprising a base;
a cover mounted on the base r the base and cover defining
a hollow interior of the trap; a casing within said
interior fast with the base and cover; a housing movably
mounted in the casing; resilient means urging the housing
J 25 to seat in the casing; a balanced pressure thermostatic
element mounted in the housing; a valve member carried
by the thermostatic element; an inlet port to said
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interior' an outlet port from said interior; and a valve
seat in the outlet port; the casing locating the housing
and the thermostatic element with respect to the outlet
port so that the valve member carried by the thermostatic
element co-operates with the valve seat in the outlet
port for opening and closing the trap; the element
defining an internal void that is open to steam/condensate
within the trap and that is sealed from the interior
of the housing in which the element is mounted; the
housing having its interior sealed from said interior
of the trap and containing volatile fluid which entirely
fills the housing outside the element when the trap is
fully open thereby to support the element; the element
being moved by the pressure exerted by the volatile fluid
upon heating of the fluid to urge the valve member carried
by the element on to the valve seat to close the trap
with the element, in the trap fully-closed condition,
being in a nearly nesting condition; the housing moving
away from its seating condition in the casing, against
the action of said resilient means; to permit the element
to adopt a fully nesting condition if further heating
of the volatile fluid occurs. The thermostatic element
may be a bellows or a multi-diaphragm arrangement. In
such a trap the thermostatic element has a fast, positive
response to temperature and pressure changes but can
withstand severe over-pressurisation due either to water-
hammer or superheat, either of which conditions may occur
in a steam system. In the case of waterhammer, during
which high hydraulic pressure can be generated inside
the element, the element is supported against deformation
by the volatile fluid. If super-heating occurs causing
the volatile fluid to generate high pressure outside
the element, the element fully nests in which condition
it can withstand great pressure.
` 35 For a better understanding of the invention
and to show how the same may be carried into effect,
reference will now be made, by way of example, to the
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2a
accompanying drawings, in which:-
Figure 1 is a somewhat diagrammatic sectionalside view of part of a steam trap, and
Figures 2A and 2B are similar views of the
major parts of two further forms of steam trap.
The steam traps shown in the Figures are balanced
pressure thermostatic traps having a ~ase which carries
the thermostatic element of the trap. In the trap of
Figure 1 this element is in the form of a bellows 2 having
rigid end walls 3 and 4 ana a side wall 5 that can shorten
or lengthen. The bellows 2 is disposed within a housing
6 with its lower end wall 3 fast with a bottom wall 7
of the housing 6. The upper end wall 4 is free to move
up and down in the housing 6.
The housing 6 is disposed within a casing 8
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that is mounted on a spigot lA on the base 1, the
housing 6 being held against a flange 8A of the casing
8 by an overload spring 9 acting between a further
flange 8B of the casing 8 and a flange 6A of the
housing 6.
The interior void 10 of the bellows 2 is open
to the casing 8 below the flange 8A via an aperture 11 in
the housing wall 7, the connection between the bellows
end wall 3 and the housing wall 7 sealing the inte~ior
of the housing 6 (outside the bellows 2) from the casing
8. Below the aperture 11 there is a valve-seat 12, formed
in the spigot lA, on which can seat a valve member 13
that is carried by a stem, 14 depending from the upper
bellows wall ~ and extending throu~h the aperture 11
so that the v~lve member 13 moves with the upper wall 4.
The interior of the housing 6, outside the
bellows 2, is filled with volatile fluid 15.
The casing 8 is contained within a cover 18
that is mounted on the base 1 so that the interior of the
trap is sealed from the atmosphere. Ports 16 in the
casing 8 below the flange 8A place the interior of this
part of the casing 8 in communication with the interior
of the cover 18.
In service the trap is mounted in a steam flow
line'~vith a port 19 in the base l in connection with the
flow line. In operation, before steam is turned on,
the trap adopts the condition shown in Figure 1-b,ellows
2 expanded, valve 12/13 open, housing 6 seated on
flange 8A. When the steam is first turned on
condensate passes through the port 19 into the
interior of the cover 18 and, via the ports 16, out ~--
through the port 17 at the valve seat 12. As warmer
condensate reaches the trap,heat is transmitted to
the volatile fluid 15 which expands with the result that
the bellows 2 begins to be forced to c~llapse thereby
moving the valve member 13 closer to the valve seat 12.
At a predetermined temperature t below the saturated
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steam temperature corresponding to the pressure at the
trap, the volatile fluid 15 boils and begins to exert
vapour pressure. When the inside of the bellows
2 is at steam pressure, the outside, because of the
termperature head, is at a pressure which is higher
by an amount p. This excess pressure forces the bellows
2 to collapse further and hence forces the valve member
13 down onto its seat 12. Thus the trap closes
just before steam temperature is reached. Condensate
is then held up in the trap until it has cooled to the
temperature t below steam temperature. At this point
the vapour pressure in the housing 6 is less than the
steam pressure inside the bellows 2 so that the bellows
2 is able to expand again and the valve member 13
therefore lifts off the valve seat 12.
The volatile fluid can be a mixture of water
and another fluid having a boiling point less than
water.
The volatile fluid is selected such that the
graphs (pressure against temperature) of the volatile
fluid and of water alone are nearly parallel and
therefore, no matter w~at the steam pressure may be in
the trap, at substantially any temperature t below the
saturated steam temperature the volatile fluid begins
to boil to cause the trap to shut~ ~`
It is to be noted in the trap of Figure 1 it
is arranged that when the bellows 2 is fully expanded -
trap fully open - the volatile fluid 15 completely
fills the interior of the housing ~ outside the bellows
2. Thus in this condition the bellows 2 is fully
supported and a surge in line pressure, due for example
to waterhammer, is prevented from expanding the bellows
further. The bellows cannot be overstretched and so cannot
be damaged by waterhammer.
, 35 In the other extreme condition - trap fully closed
bellows fully collapsed - it is arranged that the leaves
of the bellows 2 are then very nearly touching. If super-
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heated steam is present, having the ef~ect of vapouris -
ing the volatile fluid still further, the small amoun-t
of movement necessary to permit the leaves of -the
bellows fully to nest as a result of this further
heating is taken up by the housing 6 lifting off
the flange 8A against the action of the overload spring
9. Thus excessive pressure of the volatile fluid
caused by overheating causes the bellows to adopt a
fully nested condition and once this is reached the
bellows can withstand great pressure without
damage.
Figures 2A and 2B show balanced pressure
thermostatic traps having thermostatic elementsthat
are multi-diaphragm arrangements 2A (Figure 2A)
or 2B (Figure 2B), the traps otherwise being the
same æs the trap of Figure 1. Thus in each case there
are two diaphragms 23, 24 sealed to one another
at their peripheries so as to define an interior
void 10 that is open to the casing 8. As in
the case of the trap of Figure 1, the lower diaphragm
23 is fast with the bottom wall 7 of the housing 6
whilst the upper diaphragm 24 is free to move up and
do~n and carries the valve member 13~ The interior of
the housing 6, outside the diaphragm arrangement 2A or
2B; is filled with volatile ~luid 15 and each of these
traps operates in the same way as the trap of Figure
1. `
In the Gase of Figure 2A each diaphragm 23,24
is of frusto-conical form in its relaxed condition. The
diaphragms 23,24 of Figure 2B are of ~orrugated form.
As in the case of Figure 1, in the trap fu~-ly
open condition the diaphragm arrangement 2A or 2B is
fully supported by the volatile fluid which completely
fills the interior of the housing outside -the diaphragm
arrangement in this condition. In the trap fully
closed condition the individual diaphragms are nearly
touching, and fully nest if further heating occurs.
