Background of the Prior Art Numerous types of mechanical and electrical pressure indicators are known in the prior art. This is also true of pressure indicators, generally known as re¬ striction indicators, which are used to indicate flow restriction within an air filter. Restriction indicators are particularly useful for indicating a buildup of contam- inants within air filter media, particularly within air filter media utilized in an internal combustion engine.

One type of restriction indicator which is used with internal combustion engine air filters is a maximum restriction indicator. In a maximum restriction indicator, an indicator device becomes locked in a single maximum position. The locking position of the maximum restriction indicator is calibrated to indicate when the air filter media has been clogged with an undesirable amount of con¬ taminants. Thus, prior to such an indicator reaching its maximum locked position, the amount of contamination of the air filter media cannot be readily determined from the restriction indicator. U.S. Patent No. 3,068,831 to Witchell; U.S. Patent No. 3,258,960 to Baden et al; and U.S. Patent No. 3,443,365 each disclose maximum restriction indicators.

Another type of restriction indicator is a con¬ tinuous readout or dial gauge type. This type of restric¬ tion indicator can either provide - a reading only when a vacuum is applied or can have a continuous locking mecha-

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nism for locking an indicator at a plurality of point The continuous locking feature has the advantage of permi ting an operator to determine the condition of an a filter media without turning on the internal combusti engine. The continuous locking readout indicators of whi the applicant's are aware, however, do not provide f releasing of the locking mechanism from the same face the indicator from which the indicator is read. Continuo readout type indicators are illustrated in U.S. Patent No 3,939,457 and 4,033,733 to Nelson and in West German Offe legungsschrift 2617972.

Summary of the Invention The present invention is directed to a pressu sensitive indicating device. The device includes a housi defining a primary chamber. The primary chamber has first end, a second end and an axis extending between t ends. A movable member is supported in the primary chamb for motion therein. The movable member has a first si disposed in said primary chamber and a second side dispos outside the primary chamber. A first aperture is formed the housing for providing fluid communication between t primary chamber and the exterior of the housing. A biasi means biases the movable member toward the first end of t primary chamber. An indicator means is coupled to t movable member for movement therewith to indicate t position of the movable member within the primary chamb in response to fluid pressure applied to at least one the sides of the movable member. The indicator means visible from a viewing face of the housing and the viewi face is transverse to the primary chamber axis. A relea able locking means locks the movable member and the indic tor means against the biasing force of the baising means a plurality of positions along the path of travel of t movable member toward the second end of the primary cha ber. A release means is provided for releasing the locki means in order to allow the movable member to move towa the first end of the primary chamber under the biasi force of the biasing means. The release means extends

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generally transverse to the axis of the primary chamber and is actuatable from the viewing face of the housing.

In a preferred embodiment the primary chamber has a generally cylindrically shaped portion. The cylindrical portion of the primary chamber defines the first end, the second end and the axis of the primary chamber. The mov¬ able member is comprised of a hollow bellows-type diaphragm which has a first axial end secured to the housing adjacent the first end of the primary chamber's cylindrical portion and a second end received within the cylindrical portion for extending and retracting movements therein along said axis. The second axial end of the diaphragm is sealed to form a secondary chamber within the hollow interior of the diaphragm. A second aperture provides fluid communication between the secondary chamber and the exterior of the housing. A follower element is supported in the primary chamber's cylindrical portion and is coupled to the second axial end of the diaphragm for reciprocal motion therewith. The indicator means is coupled to the follower element for movement therewith to indicate the position of the follower element within the cylindrical portion of the primary chamber in response to fluid pressure applied to at least one of the apertures. In a preferred embodiment, the indicator means includes an indicator needle which is pivotable about an axis generally transverse to the axis of the cylindrical portion. The indicator needle is disposed within an indi¬ cator portion of the primary chamber. The indicator por- tion of the primary chamber is an extension from one side of the cylindrical portion. The locking means includes a plurality of first ratchet teeth which extend from a por¬ tion of the follower element and one or more second ratchet teeth movably supported in the primary chamber. The second ratchet teeth are ^' affixed in the axial direction of travel of the follower element and are movable into and out of engagement with the first ratchet teeth. The first and second ratchet teeth are arranged to permit motion of the follower element in a direction against the biasing force

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of the biasing means and to lock the follower eleme against motion in the direction with the biasing force the biasing means. The release means includes a reset r which extends generally transverse to the axis of t primary chamber and has a ramp section adjacent the seco ratchet teeth. The reset rod is movable toward and aw from the second ratchet teeth whereby the ramp secti moves the second ratchet teeth out of engagement with t first ratchet teeth when the reset rod is actuated. this manner, the biasing means is then free to move t follower element.

In another embodiment of the invention, t indicator needle is fixedly secured to a rotatable ro The rotatable rod has a first end disposed outside t housing and a second end disposed within the primary cha ber. A plurality of first ratchet teeth extend from member which is fixedly attached to the second end of t rotatable rod. The first ratchet teeth and the rod a thus rotatable in unison. A plurality of mating seco ratchet teeth are fixedly secured in position within t primary chamber. The first and second ratchet teeth ma with one another. The linear reciprocal movement of t follower member is converted into pivoting motion of t indicator needle and also into rotary motion of the rod a the first ratchet teeth. The first and second ratch teeth in their engaged position allow the motion of t follower element against the bias of the first biasi means but not with the bias of the first biasing means. Various advantages and features of novelty whi characterize the invention are pointed out with particula ity in the claims annexed hereto and forming a part hereo However, for a better understanding of the invention, i advantages, and objects obtained by its use, referen should be had to the drawings which form a further pa hereof, and to the accompanying descriptive matter, which there is illustrated and described a preferred e bodiments of the invention.

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Brief Description of the Drawings FIGURE 1 is a front elevational view of an indi¬ cating device in accordance with the present invention; FIGURE 2 is a rear elevational view of the device shown in FIGURE 1;

FIGURE 3 is a side elevational view of the device shown in FIGURE 1;

FIGURE 4 is a side elevational view of a pressure sensitive indicating device having an alternate aperture mechanism;

FIGURE 5 is a sectional view taken along line 5-5 of FIGURE 4;

FIGURE 6 is a sectional view taken along line 6-6 of FIGURE 1;

_^ FIGURE 7 is a sectional view taken along line 7-7 of FIGURE 6;

FIGURE 8 is a sectional view taken along line 8-8 of FIGURE 3; FIGURE 9 is a sectional view taken along line 9-9 of FIGURE 6;

FIGURE 10 is a sectional view similar to FIGURE 6 of another embodiment of the present invention;

FIGURE 11 is a sectional view taken along line 11-11 of FIGURE 10;

FIGURE 12 is a sectional view taken along line 12-12 of FIGURE 10;

FIGURE 13 is a sectional view taken along line 13-13 of FIGURE 10; and FIGURE 14 is a sectional view taken along line

14-14 Of FIGURE 10.

Detailed Description of the Invention Referring to the drawings in detail, wherein like numerals indicate like elements, there is shown in FIGURE 1 a pressure sensitive indicating device designated generally as 10. The device 10 includes a housing 12 which has a front face 14, a back face 16, a top face 18, a bottom face 20, and a pair of opposing side faces 22, 24. As is best seen in FIGURES 6 and 8 a primary chamber 26 is formed

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within the housing 12. The primary chamber 26 is divid -into a generally cylindrical portion 26a and an indicat portion 26b which extends from a side of the cylindric portion 26a. The cylindrical portion 26a has a first e 28 adjacent the side face 22 and a second end 30 adjace the side face 24. A longitudinal axis, shown as arrow 3 extends between the first and second ends 28, 30. T first and second ends 28, 30 can be considered ends of t primary chamber 26 and the axis 32 can be considered t axis of the primary chamber 26.

A diaphragm 34 is supported within the prima chamber 26. The diaphragm 34 serves as a movable memb which is movable within the primary chamber in response fluid pressure. The diaphragm 34 is a hollow bellows-ty diaphragm which has a generally circular cross-section a a long travel. The diaphragm 34 is preferably made of flexible elastomeric material. The diaphragm 34 has a fir axial end 36 and a second axial end 38. The diaphragm is generally coaxially aligned with the axis 32. The fir axial end 36 of the diaphragm 34 has an opening 40 and t second axial end 38 is sealed. The second axial end 38 sealed by forming the second axial end 38 as an integr closed end with the remainder of the diaphragm 34. secondary chamber 42 is thus formed within the holl interior of the diaphragm 34.

The diaphragm 34 is secured within the prima chamber 26 by attaching the first axial end 36 to t housing 12. The first axial end 36 is attached to t housing adjacent the first end 28 of the cylindrical po tion 26a by means of a retainer ring 44, a filter eleme 46, and a cap 48. The retainer ring 44 contacts or secured to a ledge 50 of the housing 12. A lip 52 of t first axial end 36 is received within an annular recess the retainer ring 44. The filter element 46 is received top of the first axial end 36 and covers the opening 40 the secondary chamber 42. The cap 48 has a top section and a generally cylindrical section 56. The top section is received on top of a major surface of the filter eleme 46 and the cylindrical section 56 surrounds the outer

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circumference of the filter element 46, the lip 52 and the retainer ring 44. The cylindrical section 56 of the cap 48 is secured to the ledge 50 and an inner wall 58 of the housing 12. In the preferred embodiment, the housing 12, the retainer ring 44 and the cap 48 are made of a plastic material. The cap 48 is secured to the housing by any suitable means, such as by glue.

A follower element 60 is received generally about the second axial end 38 of the diaphragm 34. The follower element is comprised of a generally cup-shaped member which has a generally circular base 62 and a generally cylindri¬ cal portion 64. A first arm 66 and a plurality of addi¬ tional arms 68, 70, and 72 extend radially outward from the cylindrical portion 64. The first arm 66 has a first section 74 which extends radially outward from the cylin¬ drical portion 64 in a direction generally perpendicular to the axis 32 and a second section 76 which extends from the first section 74 toward the second end 30 and generally parallel to the axis 32. The additional arms 68-72 simil¬ arly have first sections 78 and second sections 80. A gap 82 is formed between each second sections, 76, 80 and the cylindrical portion 64. The first arm 66 is slidably supported between a pair of ribs 67, 69 and each additional arm 68, 70 and 72 is slidably supported between a pair of ribs 71, 73. The ribs 67-73 are all formed integral with the housing 12.

A coil spring 84 is supported within the primary chamber 26 and comprises a biasing means for biasing the follower element 60 and the second axial end 38 of the diaphragm 34 toward the first end 28 of the cylindrical portion 26a. The spring 84 provides a calibrated biasing force which is calibrated to the range of pressures which will be read by the device 10. The range of pressures which can be read by the device 10 can thus be changed by changing the spring 84 to a spring calibrated to the new desired range. A first end of the spring 84 contacts an interior wall of the housing 12 adjacent the second end 30 of the cylindrical portion 26a. A second end of the coil

spring 84 is received within the gaps 82 and contacts t - follower element 60. In this manner, the coil spring biases the follower element 60 and the second axial end of the diaphragm 34 toward the first end 28.

An indicator means 86 is coupled to the first a 66 of the follower element 60. As will be explained mo fully hereinafter, the indicator means 86 provides indication of the relative position of the follower eleme 60 within the primary chamber 26 in response to pressu applied to one or both of the chambers 26, 42. The ind cator means 86 is carried within the indicator portion 2 of the primary chamber 26 and can be seen from the fro face 14 of the housing. The front face 14 forms a viewi face for the indicator device 10. The front or viewi face 14 is disposed transverse to the axis 32. A transpa ent cover 88 is attached to the housing 12 along its fro face 14. The cover 88 is preferably glued to a annul ridge 90 formed along the front face 14. The transpare cover 88 thus seals the primary chamber 24 along the fro face 14. A plate 92 is disposed inward of the transpare cover 28 and contacts tabs 93 which are formed integr with the housing 12 adjacent its front face 14. The pla 92 has a scale or calibrated gradations marked on its out face. The scale on the face 92 ^' coincides with the cal brated biasing force of the spring 84. When the spring is changed to provide a biasing force in a different rang the scale or plate 92 must be accordingly changed. T scale will indicate a positive or negative pressure or pressure differential, dependent on the manner in which t indicator device 10 is used. The various modes of use the device 10 will be explained more fully hereinafter.

A generally U-shaped mounting bracket 94 provided for mounting the device 10. As seen in FIGUR 1-3 and 8, the device 10 is mounted within a hole through wall 95. In the preferred embodiment, the wall 95 would a portion of a dash of a vehicle driven by an intern combustion engine. The viewing face 14 of the device can best be viewed from the interior of such a vehicle.

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The bracket 94 has a pair of arms 96, 98 that are connected by a base 100.- A pair of holes 102, 104 are formed through the base 100. An angled clamping member 106 is received through each of the holes 102, 104. Each of the clamping members 106 has a first arm 108 which is received within a recess 110 formed in the housing 14 at its back face 16. A second arm 112 extends generally perpendicularly from the first arm 108 and passes through one of the holes 102, 104. A nut 114 is threaded on each of the second arms 112. To attach the device 10 to the wall 95, the housing 12 is passed through the hole in the wall 95 until an annular rim 116 of the transparent cover 88 contacts a resilient seal¬ ing ring 97 which is interposed along an outer surface of the wall 95. Thereafter, the mounting bracket 94 is placed about the housing 10 and the first arms 108 of the clamping members 106 are placed within the recesses 110. The nuts 114 are tightened down upon the second sections 112. In this manner, the clamping members 106 pull the housing 12 through the hole in the wall 95, that is, in the direction to the left in FIGURE 8 so that the rim 116 compresses the sealing ring 97 against the outer face of the wall 95. The tightening of the nuts 114 also forces the legs 96, 98 into contact with the inner surface of the wall 95. The device 10 is thus mounted to the wall 95.

In the preferred embodiment, the indicator device 10 is used to sense a negative pressure applied to the pri¬ mary chamber 26. To apply a negative pressure to the primary chamber 26, a first aperture means, designated generally as 118, provides fluid communication between the primary chamber 26 and the exterior of the housing 12. The aperture means 118 includes a bore or hole 120 through the housing 12 between its back face 16 and the primary chamber 26 and a connecting conduit 122 coupled to the bore 120. The conduit 122 connects the indicating device 10 with a source of negative pressure. The secondary chamber 42 is open to atmosphere through the opening 40, the filter element 46 and apertures 124 through the cap 48. When negative pressure is applied through the conduit 122, the

follower 60 and the axial end 38 are free to move again the bias of the spring 84 since the chamber 42 is open atmosphere. The negative pressure must, of course, sufficient to overcome the bias of the spring 84. The bo 120 has a first section 126 with a relatively large dia eter and a tapering section 128 with a diameter whi tapers down to a small restricted orifice 130. The r stricted orifice 130 is provided for dampening any sudd pressure changes within the conduit 122 so that large a sudden fluctuations of pressure are not applied to t primary chamber 26.

In a preferred embodiment, the source of negati pressure in the conduit 122 is from an airstream passi through an air filter of an internal combustion engine. dirt collects upon the air filter, more force is requir to draw the air through the filter and hence the airstre creates a greater negative pressure in the conduit 12 This greater negative pressure draws the follower eleme 60 against the bias of the spring 84 and is sensed by t indicating means 86 in a manner explained hereinafter.

FIGURES 4 and 5 illustrate a way of adapting t device 10 to sense positive pressure applied to the secon ary chamber 42 or to sense a pressure differential betwe the primary and secondary chambers 26, 42. To accompli this, the cap. 48 is replaced with a cap 132. Since a other parts of the device 10 are the same within FIGURES and 5 the same numerals will be used to indicate the sa elements of the device 10. The cap 132 has a restrict orifice or conduit 134 formed through it. The restrict orifice 134 communicates directly with the opening 40 in the secondary chamber 42. A connecting conduit 136 coupl the restrictive orifice 134 to a source of positive pre sure. Positive pressure applied through the connecti conduit 136 is used to move the second axial end 38 and t follower element 60 against the bias of the coil spring 8 The cap 132 also taps the indicator device for use as pressure differential indicator. Alternatively, one sour of fluid pressure can be coupled to the conduit 136 to be

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applied to the secondary chamber 42 and a second source of pressure can be coupled to the conduits 122- to be applied to the primary chamber 26. In this manner, the indicator means 86 would indicate a pressure differential between the pressures applied to the conduits 122 and 136.

The indicator means 86 includes an indicator needle 138 pivotable about an axis transverse to the axis 32 of the primary chamber portion 26a. A generally cylin- drical mounting member 140 and a coupling pin 142 are formed integral with the indicator needle 138. A plug member 144 is attached within the primary chamber 26 adja¬ cent the front face 14. The plug member 144 has a curved section 146 which is best seen in FIGURE 9. The mounting member 140 of the indicator means 86 is received about the curved section 146. In this manner, the indicator needle 138, the mounting member 140 and the coupling pin 142 are pivotably supported about an axis shown as arrow 148 in FIGURE 6. The coupling pin 142 extends generally transverse to the axis 32 and radially inward toward the follower element 60. An arcuate slot 149 is formed in the housing 12 and slot 150 is formed in the second section 76 of the first arm 66. The coupling pin 142 passes through the slot 149 is received within the slot 150. In this manner, any linear reciprocal movement of the follower element 60 is converted into pivotal motion of the indicator needle 138 about the axis 148.

A releasable locking means, indicated generally as 152 in FIGURE 7, locks the follower at a plurality of positions in its travel from the first end 28 toward the second end 30 through the primary chamber 26. The indica¬ tor needle 138 is thus locked in a maximum position to which it has moved even after the pressure applied to one of the chambers 26, 42 has been removed. The locking means 152 is comprised of a plurality of first ratchet teeth 154 formed on the first arm 66 and a pair of mating second ratchet teeth 156 formed on a slide member 158. The slide member 158 is biased upwardly by a spring 160 into a posi-

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tion wherein the second ratchet teeth 156 engage the fir ratchet teeth 154. The spring 160 is comprised of a fle ^" ible wire or rod 162 and a mounting block 164. The spri 160 is bent upwardly to provide an upward biasing force the slide member 158. The mounting block 164 and the fle ible wire 162 are received within a groove 166 in t housing 12. As seen in FIGURE 7, a top surface of both t groove 166 and the mounting block 164 are flat in order align the flexible wire 162 in the upwardly bent positi shown in FIGURE 6. With the slide member 158 biased u wardly, the first and second ratchet teeth 154, 156 perm the motion of the follower element 60 toward the second e 30 against the biasing force of the coil spring 84, th is, to the right in FIGURE 7. However, the first a second ratchet teeth 154, 156 in their engaged position not permit the follower element 60 to move toward the fir end 28 under the biasing force of the coil spring 84. Th is accomplished in the conventional manner by arranging t angled and perpendicular surfaces of the ratchet teeth 15 156 in the direction shown in FIGURE 7.

A release means, designated generally as 168 FIGURE 6, is provided for moving the second ratchet tee 156 out of engagement with the first ratchet teeth 154 order to permit the follower element 60 to be moved towa the first end 28 under the biasing force of the coil spri 84. The release means 168 is comprised of a first ra section 170 on the slide member 158 and a mating seco ramp section 172 on a reset rod 174. The reset rod 174 h a first end 176 which extends outward of the housing 12 a the transparent cover 88. A flexible cap or seal 178 secured within a hole in the cover 88. The cap 178 has hole through which the first end 176 of the rod 174 passe The cap 178 performs a dual function. First of all the c 178 forms an airtight seal between the primary chamber and the outside atmostphere. The airtight seal is form both between the hole through the cover 88 and the ho through which the rod 174 passes through the cap 17 Secondly, the cap 178 serves as a biasing member which

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- - biases the reset rod 174 to the right in FIGURE 6 wherein the mating ramp sections 170, 172 are out of contact. An inner surface of the plug member 142 acts as a stop for preventing the motion of the rod 174 any further out of the housing 12. As seen in FIGURE 6, a portion of the rod 174 adjacent the ramp section 172 contacts a portion of the plug member 142 in the outermost disposition of the rod 174. In this outermost disposition the ramp section 172 is held out of contact with the ramp section 170, yet in close proximity thereto.

The reset rod 174 has a second end 180. The second end 180 passes through a slot 182 in the slide member 158 and is received within a recess or groove 184 in the housing 12. The rod 174 also passes through a hole 186 in the plug member 144. As seen in FIGURE 7, the rod 174 has a square cross-section at the ramp section 172 which mates with a rectangular cross-section of the slot 182 to hold the rod 174 in rotational alignment. The reset rod 174 is thus aligned transversely to the axis 32 of the primary chamber 28.

In order to disengage the second ratchet teeth 156 from the first ratchet teeth 154, the reset rod 174 is pushed inwardly against the bias of the cap 178. In this manner, the angled surface of the ramp section 172 contacts the angled surface of the ramp section 170 and cams or. slides the slide member 158 downwardly against the bias of the flexible rod 162. The follower member 60 is thus free to move with the biasing force of the coil spring 84. When the indicator device 10 is used to indicate contamination of an air filter in an internal combustion engine, the indicator needle 138 will be pivoted in a clockwise direction as seen in FIGURE 1 as greater negative pressure is applied to the primary chamber 26. The indica- tion of maximum negative pressure within the chamber 26 will remain indicated on the calibrated face plate 92 even when the internal combustion engine is shut off through the action of the releasable locking means 152. When a maximum amount of contamination has been indicated and the air •

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filter has been replaced, the reset rod 174 is depressed order to permit the needle 138 to be pivoted countercloc wise by the motion of the follower element 60 under t biasing force of the coil spring 84. The process of co tinual locking readout of negative pressure applied to t primary chamber 26 can again begin. In other application the continuous locking of the follower element 60 and t indicator needle 138 is used to indicate maximum pressu differentials or maximum positive pressure within t secondary chamber 42.

Another embodiment of the indicating devic designated generally as 10*, is illustrated in FIGUR 10-14. Parts of the device 10' which are similar to t device 10 will be indicated in like primed numerals. most part, the device 10' is similar to the device except for a modified follower element, indicating mean releasable locking means and release means.

The follower element 60' has a first arm 20 The first arm 200 has a first section 202 extending gene ally radially and transversely from the axis of the prima chamber and a second section 204 extending generally para lel thereto. The second section 204 has a slot 206 form in it but does not have ratchet teeth extending from it. An indicator means 208 is comprised of an ind cator needle 210, a cylindrical section 212 and a coupli pin 214 each formed integrally with one another. A pl member 216 is fixedly secured within the primary chamb 26' of the housing 12' adjacent the front face 14'. T plug member 216 has a curved section 218 about which t cylindrical section 212 of the indicator means 208 rotatably received. A reset rod 220 extends from t interior of the primary chamber 26' of the housing 12' to location exterior of the housing 12' and the transpare cover 88' . The indicator means 208 is fixedly secured the reset rod 220 by splines 221 so that the indicat means 208 and the rod 220 are rotatable in unison. T coupling pin 214 passes through an arcuate slot 149' and received in the slot 206. The linear motion of the fol-

lower element 60' is transfered as pivotal motion of the indicator needle 210 through the coupling pin 214. In the device 10' the needle 210 pivots about the axis of the rod 220.

The reset rod 220 has a first end 222 which extends outward of the cover 88' and is secured in an air-tight manner to the cap 178'. The rod 220" has a second end 224 which is supported within the primary chamber 26' . of the housing 12' .

A releasable locking means, designated generally as 226, permits the movement of the follower element 60' against the bias of the coil spring 84' but locks the follower element 60' to prevent motion of the follower element 60' under the biasing force of the coil spring 84'. The locking means 226 includes a plurality of first ratchet teeth 228 which extend from a disc or member 230 and a plurality of mating second ratchet teeth 232 which extend from a second disc or member 234. The disc 234 has a pair of ears 236 which fit within mating recesses in the housing 12' . The disc 234 is thus secured against rotary motion relative to the housing 12' .

The rod 220 extends inwardly from the cover 88' and passes through a hole 225 in the plug member 216 and through a hole 227 in the disc 234. The disc 230 is fix¬ edly secured to the second end 224 of the rod 220. The disc 230 is thus rotatable in unison with the rod 220. The cap 178' biases the disc 230 outward toward the front face 14. In this manner, the first ratchet teeth 228 are biased into engagement with the second ratchet teeth 232. The ratchet teeth 228, 232 are arranged to lock the follower element 60' in the manner described above. The rod 220 also acts as a release means. By depressing the rod 220 against the bias of cap 178', the first teeth 228 can be moved out of engagement with the second teeth 232. This disengaged condition is shown in FIGURE 14. With the first and second ratchet teeth 228, 232 out of engagement, the follower element 60' is free to move under the biasing force of the coil spring 84' . The device 10' can be used

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in the same manner as the device 10 to measure positive negative pressure or pressure differentials.

The indicator devices 10, 10' have numero advantages. For example, the moving parts of the devic 10, 10' such as the follower element 60, 60', the indicat means 86, 208 and the locking means 152, 226 are on t sealed clean air side of the diaphragm 34, that is, with the primary chamber 26 and are thus sealed from outsi contamination. The use of a long travel diaphragm 34 conjunction with a calibrated spring 84 results in reado accuracy. Also, an infinite number of readout ranges c be obtained by simply changing the calibrated spring 84 a the scale on the plate 92. The use of restricted orific 130, 134 at the pressure and vacuum inlets dampens t effects of a pulsating pressure or vacuum source. Als the indicator devices 10, 10' can be easily modified serve as pressure gauges, vacuum gauges or differenti pressure gauges by the use of the cap 132 which can secured to the housing 12 or 12' by a suitable means i cluding a threaded adapter.

Numerous characteristics and advantages of t invention have been set forth in the foregoing descriptio together with details of the structure and function of t invention, and the novel features thereof are pointed o in the appended claims. The disclosure, however, is illu trative only, and changes may be made in detail, especial in matters of shape, size, and arrangement of parts, with the principle of the invention, to the full extend extend by the broad general meaning of the terms in which t appended claims are expressed.

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