US 3619526 A
Description (OCR text may contain errors)
United States Patent PRESSURE-ACTUATED SWITCHES 1 Claim, 4 Drawing Figs.
US. Cl 200/83 J,
200/82 C, 200/166 M Int. Cl H0lh 35/38 Field of Search ZOO/82.2,
 References Cited UNITED STATES PATENTS 2,898,418 8/1959 Byam 200/166 M X 3,039,833 6/1962 Farkas... ZOO/82.2 X 3,419,692 12/1968 Palen ZOO/82.2 3,444,341 5/1969 Mighton 200/822 3,412,223 11/1968 Schad Primary Examiner-Robert K. Schaefer Assistant Examinerwilliam J. Smith Attorneys-Emory L. Groif and Emory L. Groff, .Ir.
ABSTRACT: A pressure-operated electric switch, consisting of a housing having a spring loaded piston therein and a diaphragm moved by pressure change, with a microswitch having its operating pin coaxial with the piston and axially adjustable in relation to the piston, with the loading of the spring on the piston also adjustable independently of the pin to the piston.
1g 3 1 f 5 16 H 16 a 7- 12 I 10 14L g 141 I 13 ii} 15 Fig.
I H l\ ZOO/153.19
PRESSURE-ACTUATED SWITCHES BACKGROUND OF THE INVENTION This invention concerns pressure-actuated switches, that is to say, switches which are actuated according to pressure changes, for example in a vessel or pressure system, which switches can be used as safety devices or as alarm switches or for control purposes, for example in instrumentation or automation.
An object of the invention is to provide pressure-actuated switches which are of simple construction and which ensure a high degree of accuracy. Another object is to provide such switches which can be set easily to operate at a predetermined pressure, or in which the pressure can be adjusted within limits. A further object is to provide pressure switches of robust construction in which there is no possibility of the electric switch being damaged, for example by excessive overpressure.
SUMMARY OF THE INVENTION According to the invention, the switch comprises a housing, a piston in said housing for axial movement therein, a diaphragm held adjacent the head of said piston, an inlet for feeding fluid pressure on to the diaphragm, a coil spring coaxial with the piston to load same and the diaphragm against the pressure, a support mounted on said housing, a microswitch carried by said support with its operating pin coaxial with the piston means for adjusting said support axially in relation to the piston, means for adjusting the spring loading independently of the adjustment of the pin to the piston, and means for limiting movement of the piston towards the pin.
The construction according to the invention provides an arranger'nent in which the movement of the piston to operate the switch can be adjusted finely and accurately, it being understood that the movement of a microswitch operating pin for operation is small. Further, the invention provides a construction in which the limits of movement of the switch are accuratelyset, so preventing damage to the switch.
BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to the accompanying drawings, which show preferred embodiments of pressure actuated switches in accordance with the invention.
In the drawings:
FIG. 1 is a sectional elevation of one form of switch, which is preset and locked at the operating pressure.
FIGS. 2 and 3 are similar views of switches in which the operating pressure can be adjusted within limits, and
FIG. 4 is a similar view of a switch which operates at subatmospheric pressure.
Like references indicate like parts in all of the views.
DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIG. 1, the pressure switch consists of a bored stub 1 having a flange in forming a head, the stub being externally screw-threaded at lb for securing to a pressure vessel or pressure system. A housing 2 is secured to the flange head 1a by means of a swaged over rim of the flange. Altematively and as shown in FIG. 3, the flange and housing could be secured together by bolts 4. A diaphragm 3 is secured between the flange and housing, a spacer ring 5 being interposed. The diaphragm conveniently is of nitrile or butyl rubber. A sealing ring 6 is also provided. The upper face of the diaphragm 3 is acted on by pressure in the vessel or system, and a piston 7 is provided in the housing, the top of which bears on or is attached to the lower face of the diaphragm.
The'piston can slide in .an upper cavity of the housing 2, its downward limit of movement being set by a shoulder or shelf 8 and its upper limit by abutment of the ring 5 cooperating with a shoulder 7a of the piston, the downward piston movement being opposed by a coiled spring 9. The lower end of the spring bears on the bottom of a casing 10 screw threaded on to the housing 2 at 11, so that axial adjustment of the housing 2 and casing 10 can be made to adjust the spring loading. The end of the piston extends through an aperture through the bottom of the casing.
A microswitch 12 with an actuating or operating pin 12a is secured to a support 13, which support 13 engages the casing 10 by screw threads 14. The switch is housed within a cover 15.
It will be understood that it is necessary for the accurate axial movement of the pin 12a to be obtained, and that its total movement is small, for example from its upward position it moves about 0.004 inch to changeover, and further movement must not exceed about 0.001 inch. The constructions according to the invention permit accurate setting with no possibility of excess pressure on the pin 12a.
The switch is adjusted by firstly screwing down the casing 10 to release spring pressure on the piston, and the desired actuating pressure is then applied through the stub I on to the upper face of the diaphragm. The casing 10 is then screwed up slightly (about 0.001 inch) and the support 13 is screwed up the casing 10 until the switch just operates by contact with the lower end of its piston. The parts 2, l0, and 13 are then locked up, for example by grub screws or by synthetic plastic inserts in the threads or by filling with epoxy resin.
In use, at suboperating or changeover pressure, the parts are in the positions shown. As the pressure increases, the piston 7 moves. down and at the operating pressure the switch is operated. It will be seen that even if this pressure is greatly exceeded', themicroswitch'can move down no more. than the amount by which the casing 10 was screwed upon adjustment, as the piston is stopped by the shoulder 8. Further, upward spring pressure cannot damage the diaphragm as the shoulder 70 on the piston, by abutment with the ring 5, limits upward piston movement.
In the construction shown in FIG. 2, after initial adjustment, the operating pressure can be adjusted in use. In this arrangement a cover part 15a carries the microswitch support 13, which support 13 engages the housing 2 by screw threads 14, and the cover part 15a is arranged so that it can be secured to the housing 2, for example by grub screws 16 engaging on the swaging of the head In. The switch is initially adjusted as above described, except that the screws 16 are loosened so that the axial position of the cover part lSa relative to the housing 2 is adjusted to set the pin 12a in relation to the end of the piston 7, the screws being tightened after engagement. The part 150 can slide on the head, as shown, or engage same by screw threads, or the housing 2 as shown in FIG. 3.
The screw threads 11, 14, are of identical pitch so that the casing 10 can later be adjusted in relation to the housing 2, enabling the operating pressure to be adjusted within limits.
The switches shown in FIGS. 1 and 2 are intended to operate at pressures up to about p.s.i. The switch shown in FIG. 3 is intended to operate at higher pressures, for example up to 500 p.s.i. The construction of FIG. 3 is generally similar to that of FIG. 2, except that the cover 15a is replaced by a housing part 17 which screw-threads on to the housing 2 and also on to the casing 10. The part 17 can be locked by grub screws 16a to the housing 2 after adjustment of the piston in relation to the pin 12a .As the casing 10 engages in the housing 17 by screw threads 140, the spring pressure can be adjusted without upsetting the pin and piston adjustment.
The above-described embodiments operate at supratmospheric pressure and FIG. 4 shows a construction for operation at subatmospheric pressure. In this construction the housing 2 engages in the flange 1a by screw threads 18, the stub I forming the stop for the upper end of the spring 9. The casing 10a is secured to the housing 2, and a plunger 19 is secured to the lower face of the diaphragm 3, the lower end of this plunger cooperating with the pin 12a of the microswitch. The spacer ring 5 and sealing ring 6 are between the parts 2 and 10a. The support 13 and easing 10a are relatively adjustable by screw threads 14b, as are the stub flange head la which forms a casing supporting the spring and housing 2, by the screw threads 18, so that adjustment of the distance of the microswitch pin 12a from the plunger end, and of the spring pressure on the diaphragm can be adjusted. The spring pressure can be adjusted without upsetting the switch pin adjustment or the distance of travel of the piston.
ln all of the embodiments, in order to avoid damage to the diaphragm, the gap between the spacer ring and piston should be small and the inner edge of the ring rounded or beveled ofi'. [t is not essential for a spacer ring to be provided as the diaphragm can be clamped directly between the stub flange la and the housing 2. The edges of appropriate parts adjacent the piston will in this case also be rounded or beveled.
l. A pressure-actuated switch comprising a housing, a piston in said housing for axial movement therein, a diaphragm held adjacent the head of said piston, an inlet for feeding fluid pressure on to the diaphragm, a coil spring coaxial with the piston to load said piston and the diaphragm against the pressure, a support mounted on said housing, a microswitch including an operating pin carried by said support, said operating pin coaxial with the piston, means for adjusting said support axially in relation to the piston when said switch is assembled, said adjusting means comprising a casing screw-threaded to said housing for loading adjustment of the spring, said support engaging said casing by screw threads so as to be axially adjustable in relation thereto, said piston extending through the casing for engagement with the switch operating pin, means for limiting movement of the piston towards the pin, means for adjusting the operating pressure while said switch is in use, said means including a cover member to which said support is secured, said cover member secured to said housing and axially movable relative thereto, whereby said operating pin may be set in relation to the adjacent end of said piston.