Adjustable magnification fogless mirror

A mirror ideally suited for use in a shower enclosure, bathroom or other high humidity environment is adjustable by a user to provide a magnification increasable from unity to three times or more, as well as being resistant to condensation fogging of viewing surfaces thereof. A fogless adjustable magnification mirror according to the present invention includes a ring-shaped frame which holds within an inner peripheral wall surface thereof a clear front viewing window and a rear flexible mirror plate or diaphragm having a reflective surface and a circular shape. The viewing window and mirror plate are held within the frame in a fluid pressure-tight seal, and form therebetween a sealed hollow cylindrically-shaped interior space or plenum bordered on a peripheral longitudinal surface thereof by the inner annular surface of the frame. An inlet port which penetrates the frame and communicates with the plenum has coupled thereto a conduit adapted to be coupled at the opposite end of the conduit to a source of warm water, preferably provided by a T-fitting which fits between a shower head and water supply pipe, and which diverts a small percentage, e.g., 5% to 10% of water flowing through the T-fitting into the inlet conduit. An outlet port which penetrates the frame and communicates with the plenum is coupled at an outer end to a throttle valve which is adjustable to adjust the outlet fluid flow cross-section.

BACKGROUND OF THE INVENTION
 A. Field of the Invention
 The present invention relates to mirrors of the type used by people to
 facilitate performance of personal care functions such as shaving,
 applying cosmetics, and the like. More particularly, the invention relates
 to a novel mirror having a magnification that may be readily varied by a
 user, and which also resists formation of water condensation droplets or
 fog on the viewing surface thereof, thus permitting the mirror to function
 effectively in humid environments such as shower enclosures and bathrooms.
 B. Description of Background Art
 A substantial number of people utilize mirrors while showering to
 facilitate performance of personal care functions such as shaving.
 However, the use of mirrors in showers was formerly relatively limited,
 because the warm moist air within a shower enclosure tends to quickly
 condense on the surface of any mirror used in the shower, obscuring an
 image of a person's face reflected from the mirror surface so completely
 as to render the mirror practically useless within a few minutes after a
 shower has begun.
 In response to the problem of moisture condensing on a mirror surface and
 thereby limiting the usefulness of mirrors in high humidity environments,
 such as shower enclosures and other locations within a bathroom, the
 present inventor disclosed in U.S. Pat. No. 4,733,468, issued Mar. 29,
 1988, a "fogless" mirror which is highly resistant to formation of
 condensation droplets on the surface of the mirror. The fogless mirror
 disclosed in the '468 patent utilizes warm water tapped from the warm
 water supply pipe to a shower head, to heat the surface of the mirror.
 Since water vapor in a shower produced largely by evaporation, the water
 vapor is always somewhat cooler than the warm water supplied to the shower
 head. And, since water vapor will condense only on surfaces which are at
 lower temperature than the vapor, heating the surface of the mirror
 precludes fogging of the mirror. Therefore, the fogless mirror disclosed
 in the present inventor's '468 patent proved to be a highly effective
 solution to the problem of bathroom mirror fogging, and mirrors utilizing
 the teachings of that patent have been widely marketed and used.
 The disclosure of a practical and effective fogless mirror in the present
 inventor's '468 patent solved the problem of providing a bathroom mirror
 of unity magnification which is non-fogging. However, there are a variety
 of circumstances in which it would be desirable to have available a face
 mirror that has a variable magnification. For example, detailed hygienic
 or cosmetic functions which involve eyebrows or eye lashes benefit from
 the use of a concave magnification mirror. But, since the field of view of
 a magnifying mirror of a given size is inherently smaller than that of a
 flat, unity-magnification mirror, a magnifying mirror may be unsuitable
 for performing other functions, such as shaving, which preferably employs
 a mirror having a larger field of view which encompasses the entire face.
 Therefore, shaving and performing other such tasks related to personal
 hygiene or beautification would oftentimes be facilitated by the use of a
 mirror having multiple discrete or continuously variable magnifications.
 In response to this need, the present inventor disclosed a Variable
 Magnification Mirror in U.S. Pat. No. 5,900,996, which issued on May 4,
 1999. That patent disclosed a variable magnification mirror having a thin
 diaphragm provided with a reflective front surface and includes a
 mechanism for deforming the diaphragm from a flat shape, yielding unity
 magnification of images formed by the reflective surface, to adjustably
 greater curvatures yielding adjustably larger magnification factors. The
 mechanism includes a screw-driven, flexible circular puller plate fastened
 to a rear central portion of the rear surface of the reflective diaphragm,
 the outer peripheral edge of the diaphragm being held axially fixed with
 respect to the screw. In the preferred embodiment, the puller plate is so
 constructed as to have greater flexibility at outer radial portions
 thereof to accommodate larger angular defections of the outer radial
 portions of the diaphragm, thereby aiding in maintenance of substantially
 spherical, distortion free contour. The increased flexibility of outer
 radial portions of the puller plate is preferably effected by a radial
 taper provided in the puller plate cross section, the outer radial
 portions of the plate being progressively thinner than the central radial
 portion of the puller plate. Preferably, the puller plate is fastened to
 the rear surface of the reflective diaphragm by means of a resilient
 adhesive member, the elastic deformability of the member further aiding in
 maintenance of a substantially spherical diaphragm contour.
 Although the variable magnification mirror disclosed in the '996 patent has
 proved to be a highly effective and widely accepted solution to the
 problem of providing a variable magnification mirror useful for personal
 hygiene tasks, there is no obvious practical way to incorporate a flow of
 warm water through the device to heat the mirror surface and thereby
 resist formation of condensation droplets on the mirror surface. Thus, a
 problem still persisted, particularly for people who are unable to wear
 eyeglasses or contact lenses while showering, yet wish to shave or perform
 other personal hygiene tasks in the shower. For such individuals, it would
 be highly desirable to have available a mirror of adjustable magnification
 to compensate for vision difficulties experienced with their eyeglasses or
 contact lenses removed. In view of the foregoing facts, the present
 inventor conceived of a fogless variable magnification mirror having a
 highly novel construction and function.
 OBJECTS OF THE INVENTION
 An object of the present invention is to provide a mirror having a
 magnification that is smoothly and readily variable over a substantial
 range of magnifications, and which resists formation of condensation
 fogging on image viewing surfaces thereof.
 Another object of the invention is to provide a variable magnification
 fogless mirror which utilizes warm water to heat optical surfaces of the
 mirror above ambient atmospheric temperature, thereby minimizing
 condensation of water vapor droplets from the atmosphere onto the optical
 surfaces.
 Another object of the invention is to provide a variable magnification
 fogless mirror which utilizes hydrostatic fluid pressure supplied by
 condensation-inhibiting warming water to deform a flexible reflective
 diaphragm into a concave reflecting surface.
 Another object of the invention is to provide a variable magnification
 fogless mirror which utilizes warm water flowing in a chamber formed
 between a front viewing window and a rear flexible diaphragm having a
 mirrored surface to heat the viewing window and thereby minimize
 condensation fogging of the front surface of the viewing window.
 Another object of the invention is to provide a variable magnification
 fogless mirror including a frame forming a heated interior plenum space
 between a front viewing window and a circular rear flexible diaphragm
 having a mirrored surface, the frame having an inlet port for receiving
 warm water under pressure, and an outlet port provided with an adjustable
 flow-rate valve, whereby hydrostatic pressure within the plenum may be
 varied by adjustment of the flow-rate valve to thereby vary concave
 deformation of the diaphragm, and thereby vary its magnification to a
 selected value.
 Various other objects and advantages of the present invention, and its most
 novel features, will become apparent to those skilled in the art by
 perusing the accompanying specification, drawings and claims.
 It is to be understood that although the invention disclosed herein is
 fully capable of achieving the objects and providing the advantages
 described, the characteristics of the invention described herein are
 merely illustrative of the preferred embodiments. Accordingly, I do not
 intend that the scope of my exclusive rights and privileges in the
 invention be limited to details of the embodiments described. I do intend
 that equivalents, adaptations and modifications of the invention
 reasonably inferable from the description contained herein be included
 within the scope of the invention as defined by the appended claims.
 SUMMARY OF THE INVENTION
 Briefly stated, the present invention comprehends a fogless mirror having a
 magnification which may be readily adjusted by a user from unity to larger
 positive values, e.g., over a magnification range of one-times to
 three-times (1.times. to 3.times.), or more. A fogless mirror according to
 the present invention is of a novel design and construction which not only
 enables the magnification factor of the mirror to be readily adjusted, but
 has a further advantage of being resistant to water droplets or fog
 condensing onto the viewing surfaces of the mirror when the mirror is used
 in a humid environment such as a bathroom or shower enclosure.
 According to the present invention a fogless adjustable magnification
 mirror includes a ring-shaped, preferably circular, frame which holds in a
 first, front ring-shaped retainer groove in an inner longitudinal surface
 thereof an optically clear front viewing window. The latter preferably has
 a circular outline shape, and is made of a rigid transparent material such
 as glass or relatively thick polycarbonate or acrylic plastic, and is held
 in the front retainer groove in a fluid pressure-tight seal. A fogless
 adjustable magnification mirror according to the present invention also
 includes a flexible reflective mirror plate or diaphragm having a
 reflective surface and a circular shape. The flexible mirror plate is
 located behind the front viewing window, and is held in a fluid
 pressure-tight seal within a rear circular ring-shaped retainer groove
 provided in the inner longitudinal surface of the frame, rearward of the
 front viewing window retainer groove. Thus constructed, the mirror
 according to the present invention has formed between the front viewing
 window and rear flexible reflecting diaphragm thereof a sealed, hollow
 cylindrically-shaped interior space or plenum bordered on a peripheral
 longitudinal surface thereof by the inner annular surface of the frame.
 The mirror according to the present invention is provided with an inlet
 port for conducting warm water into the interior space of the mirror, the
 inlet port penetrating the frame and communicating with the plenum. The
 mirror also includes an outlet port for conducting water from the plenum,
 the outlet port penetrating the frame at a location spaced
 circumferentially apart from and preferably diametrically opposed to the
 inlet port. A water supply conduit for conducting warm pressurized water
 to the mirror is connected by a fluid pressure tight coupling at one end
 thereof to the inlet port. Preferably, the water supply conduit is made of
 a flexible hose or tube, and has at the other end thereof a fitting, such
 as a threaded tee, which may be installed between a water supply pipe and
 shower head, and which diverts a small percentage of water flowing to the
 shower head, e.g., 5-10%, to the mirror water supply conduit.
 The adjustable magnification fogless mirror according to the present
 invention also includes a water outlet conduit connected by a fluid
 pressure-tight coupling to the mirror outlet port. The outlet conduit,
 which is also preferably made of a flexible hose or tube, is provided with
 an in-line adjustable valve which enables adjustment of the flow rate of
 water from the mirror plenum. Warm water is supplied to the mirror by
 opening the hot and cold water supply valves to the shower head, gradually
 filling the mirror plenum with clear water. When water in the plenum has
 filled the space between the front reflective surface of the rear
 reflecting diaphragm and the rear surface of the front viewing window, the
 front reflective surface of the diaphragm, disk-shaped volume of water
 within the plenum, and front viewing window form a disk-shaped composite
 lens having a reflective rear mirror surface and no optical surface
 exposed to the air, thus precluding condensation fogging on any interior
 surface thereof. Moreover, heat conducted from warm water in the plenum
 through the viewing window to its front surface precludes condensation of
 water vapor in the shower enclosure on the front surface of the viewing
 window.
 To increase the magnification of the fogless mirror according to the
 present invention, the valve in the warm water outlet port is adjustable
 from a fully-open to a partially closed position in which the fluid-flow
 cross-section of the valve orifice is reduced to a value less than
 fluid-flow cross-section of the water inlet conduit. Reducing the flow
 cross-section reduces the outlet flow rate of water through the mirror
 plenum, causing hydrostatic pressure in the mirror plenum to increase to a
 value greater than ambient atmospheric pressure. Increased hydrostatic
 pressure within the plenum in turn causes the rear flexible mirror
 diaphragm to bow outwardly of the plenum, i.e., rearwardly, which in turn
 causes the reflecting surface of the mirror diaphragm to deform from a
 flat to concave shape. Deformation of the reflective mirror surface causes
 the magnification of the mirror to increase from a value of unity, for the
 flat, undeformed mirror diaphragm to a positive value greater than unity.
 By adjusting the valve to further restrict water flow from the mirror, the
 hydrostatic pressure may be adjusted to higher values, resulting in
 greater concave deformation of the mirror diaphragm and an accompanying
 increase in the magnification of the mirror. Moreover, since the mirror
 diaphragm is made of an elastically deformable material such as
 polycabonate plastic, opening the magnification adjustment control valve
 to allow unrestricted flow of water through the mirror decreases
 hydrostatic pressure within the mirror plenum to a value close to
 atmospheric pressure, allowing the elasticity of the diaphragm to restore
 it to its flat shape, thus restoring the magnification of the mirror to a
 value of unity. Thus, the magnification of the adjustable magnification
 fogless mirror according to the present invention may be readily adjusted,
 while optical surfaces of the mirror are kept fog-free.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIGS. 1-7 illustrate an adjustable magnification fogless mirror according
 to the present invention.
 Referring first to FIGS. 1-4, an adjustable magnification fogless mirror 20
 according to the present invention may be seen to include a ring-shaped
 frame 21 having longitudinally disposed inner and outer peripheral wall
 surfaces 22 and 23, respectively. Frame 21 is made of any suitably rigid,
 water impervious material such as metal, acrylic-plastic, or the like. As
 may be seen best by referring to FIG. 4, frame 21 has formed in inner wall
 surface 22 thereof, inwardly or rearwardly from front annular surface 24,
 a first, front, annular ring-shaped groove 25. Fitted within front groove
 25 is a circularly-shaped clear plate of uniform thickness forming a front
 viewing window 26. Front viewing window 26 is preferably made of a rigid,
 optically transparent material such as glass plate having a thickness of
 about 1/16 inch, or of polycarbonate or acrylic plastic having a thickness
 of about 1/18 inch. The outer circumferential edge wall 27 of front
 viewing window 26 is held within front annular groove 25 in frame 21 in a
 fluid pressure-tight seal, being bonded thereto by an epoxy adhesive or
 the like.
 Referring still to FIG. 4, it may be seen that frame 21 of mirror 20 has
 formed in inner wall surface 22 thereof, inwardly from rear annular
 surface 28 of the frame, a second, rear annular ring-shaped groove 29.
 Fitted within rear groove 29 is a circular mirror diaphragm 30. Mirror
 diaphragm 30 is made of a relatively thin, elastically deformable sheet of
 material such as polycarbonate plastic having a thickness of about 1/16
 inch. Also, mirror diaphragm 30 has front and rear parallel surfaces 31
 and 32, one of which is metalized to form an optically flat, highly
 reflective mirrored surface. In a preferred embodiment, mirror diaphragm
 30 is made of optically transparent acrylic or polycarbonate plastic, the
 rear surface 32 of which has vacuum deposited thereon a thin, highly
 reflective layer of aluminum forming a reflective mirror surface 33.
 Alternatively, mirror diaphragm 30 could be made of a thin sheet of
 stainless steel or other metal having a chrome plated front reflecting
 surface.
 The circumferential edge wall 34 of mirror diaphragm 30 is held within rear
 annular groove 29 in frame 21 in a fluid pressure-tight seal, being bonded
 thereto by an epoxy adhesive or the like.
 As shown in FIG. 4, front viewing window 26 of mirror 20 has a flat,
 circular rear face 35 located forward of front face 31 of mirror diaphragm
 30, forming therebetween a cylindrically-shaped interior space or plenum
 36, which has a circumferential boundary formed by inner peripheral wall
 surface 22 of frame 20. Front viewing window 26 also has a front exterior
 face 37 parallel to its rear face 35.
 Referring now to FIGS. 1-4, it may be seen that mirror 20 is provided with
 an inlet port 38 for conducting warm water from an external source such as
 a shower pipe into plenum 36 of the mirror. Inlet port 38 includes a
 hollow tubular inner portion 39 which is held within an inlet bore 40
 disposed radially inwardly from outer longitudinally disposed peripheral
 wall surface 23 of frame 21 through inner peripheral wall surface 22 of
 the frame. Inner tubular portion 39 of inlet port 38 is secured within an
 inlet bore 40 provided through frame 21 in a fluid pressure-tight seal,
 being bonded to the inlet bore wall by an epoxy adhesive or the like.
 Tubular portion 39 of inlet port 38 has through its length a
 longitudinally disposed bore or passageway 41 which communicates with
 plenum 36.
 Referring still to FIGS. 1-3, it may be seen that mirror 20 includes a warm
 water supply tube 42 which is coupled in a fluid pressure-tight connection
 at a first, inlet end 43 thereof to a source of warm water, and at a
 second, outlet end 44 thereof to hollow tubular portion 39 of inlet port
 38.
 Warm water supply tube 42 is preferably made of a flexible hose, and may be
 coupled at outlet end 44 thereof to tubular portion 39 of inlet port 38 by
 receiving the inlet tube in a fluid pressure-tight interference fit within
 a bore 45 disposed through the length of the water supply tube.
 Alternatively, outlet end 44 of water supply tube 42 may be received
 directly within inlet bore 40 though frame 21 in a fluid pressure-tight
 seal, in which case the inner end of the water supply tube serves as inlet
 portion 39 of inlet port 38.
 As shown in FIG. 1, during use of mirror 20, inlet end 43 of warm water
 supply hose 42 is coupled to a source of warm water. Thus, as shown in
 FIG. 1, inlet end 43 of warm water supply hose 42 preferably is coupled to
 the side outlet tube 48 of a T-fitting 47. The latter has an inlet tube 49
 adapted to threadingly couple to the end of the shower-head water supply
 tube A, and an end outlet tube 50 adapted to threadingly couple to a
 shower head B. As shown in FIG. 4, side outlet tube 48 of T-fitting 47 is
 of smaller diameter than the common diameters of end inlet and outlet
 tubes 49 and 50 of the fitting, and has an inner end portion 51 which
 penetrates the cylindrical body 52 of the fitting. Inner end portion 51 of
 side outlet tube 48 has an entrance opening 53 which faces upstream
 towards inlet tube 49, and is so positioned and sized as to intercept a
 small percentage, e.g., 5% to 10%, of water flowing between inlet tube and
 end outlet tube 50, diverting the intercepted portion into the bore of the
 side outlet tube.
 As shown in FIGS. 1-3, mirror 20 includes an outlet port 55 for conducting
 water out from plenum 36. Outlet port 55 includes a hollow tubular inner
 portion 56 which is held within an outlet bore 57 provided through frame
 21. As shown in FIGS. 1 and 3, outlet bore 57 is disposed radially
 outwardly from inner peripheral wall surface 22 through outer peripheral
 wall surface 23 of frame 21. As is also shown in those figures, outlet
 bore 57 is spaced circumferentially apart from inlet bore 40, preferably
 at a location offset slightly from a point diametrically opposed to the
 inlet bore 40.
 Hollow tubular inner portion 56 of outlet port 55 is secured within outlet
 bore 57 in a fluid pressure-tight seal, being bonded to the outlet bore
 wall by an epoxy adhesive or the like. Tubular portion 56 of outlet port
 55 has through its length a longitudinally disposed bore or passageway 58
 which communicates with plenum 36.
 Referring still to FIGS. 1-3, it may be seen that mirror 20 includes a
 water outlet conduit 59 which is coupled in a fluid pressure-tight
 connection at a first, inlet end 60 thereof to hollow tubular portion 56
 of outlet port 55. Water outlet conduit 59 has a second, outlet end 61
 which has a outlet opening 62 which communicates with a bore 63 that is
 disposed through the length of the outlet tube.
 Water outlet conduit 59 is preferably made of a length of flexible hose,
 and may be coupled at inlet end 60 thereof to tubular portion 56 of outlet
 port 55 by receiving the tube in a fluid pressure-tight interference fit
 within bore 63 of the water outlet tube. Alternatively, inlet end 60 of
 water outlet tube 59 may be received directly within outlet bore 57
 through frame 21 in a fluid pressure-tight seal, in which case the inner
 end of the outlet tube serves as inner tubular portion 56 of outlet port
 55.
 Referring now to FIGS. 3 and 4, it may be seen that mirror 20 includes a
 valve 64 located in series or in-line with water outlet tube 59. Valve 64
 has an internal orifice which controls the cross-section of water flowing
 through the valve, the size of the orifice and flow cross-section being
 adjustable by a control knob 65 to a value approximating that of bore 63
 through water outlet tube 59, to smaller values. Thus, valve 64 functions
 as a throttle valve, controlling the flow rate of warm water out from
 plenum 36 which is supplied to the plenum through inlet port 38.
 As shown in FIG. 1, mirror 20 includes means for mounting the mirror to a
 structural element such as a shower head water supply pipe. Thus, as shown
 in FIG. 1, mirror 20 may have a clamp 66 which protrudes upwardly from
 frame 21 of the mirror and which includes an upwardly protruding split
 ring 67 for attachment to a shower head supply pipe C. Clamp 66 is
 preferably longitudinally aligned with outlet port 55 of mirror 20. With
 this arrangement, water outlet port 55 is positioned below clamp 66, and
 offset slightly from inlet port 38, as shown in FIGS. 1 and 3.
 Functional operation of mirror 20 may be best understood by referring to
 FIGS. 4 through 7. As shown in FIG. 4, plenum 36 of mirror 20 is initially
 empty. To use mirror 20, warm water is introduced into plenum 36 through
 inlet port 38 by connecting tee-fitting 47 between a shower head water
 supply pipe A and shower head B, as shown in FIGS. 1 and 4. Warm water is
 then admitted to shower water supply pipe A by opening shower valves (not
 shown), thus gradually filling plenum 36 with water D, as shown in FIG. 5.
 During this operation, throttle valve 64 is preferably adjusted by control
 valve 64 thereof to a fully open position, e.g., counterclockwise in FIG.
 6, thereby minimizing back pressure and facilitating rapid filling of
 plenum 36 with water.
 When plenum 36 is filled with water, as shown in FIG. 6, water D within the
 plenum optically contacts rear surface 35 of front viewing window 26 and
 front surface 31 of mirror diaphragm 30, thus forming a void-free liquid
 lens which precludes formation of any condensation droplets on either of
 those two surfaces. Moreover, heat conducted from warm water D within
 plenum 36 through front viewing window 26 to front face 37 of the viewing
 window raises the temperature of the front viewing window surface above
 the dew point of moist air within the shower enclosure, thus precluding
 fogging of the front surface of the mirror.
 With throttle valve 64 in a fully open position as shown in FIG. 6, front
 and rear surfaces 31 and 32 of mirror diaphragm 30 are flat and parallel
 to front and rear surfaces 37 and 35 of front viewing window 26. Thus
 configured, mirror 20 has a unity or 1.times. magnification.
 To increase the magnification of mirror 20 to a factor greater than one,
 control knob 65 of throttle valve 64 is turned in a direction, e.g.,
 clockwise in FIG. 7, which reduces the fluid-flow cross-section of the
 valve to a value less than that of warm water inlet port 38. Reduction in
 fluid-flow cross-section of output port 55 relative to inlet port 38
 causes the hydrostatic pressure of water D within plenum 36 to increase
 above ambient atmosphere pressure. This pressure increase within plenum 36
 causes flexible mirror diaphragm 30 to bow outwardly of plenum 36, i.e.,
 rearwardly as shown in FIG. 7. Thus, reflective surface 33 of mirror
 diaphragm 30 is deformed by an increase in hydrostatic pressure within
 plenum 36 from a flat surface as shown in FIG. 6, to the concave surface
 shown in FIG. 7. Deformation of reflective surface 33 to a concave shape
 causes the magnification of the mirror to increase from a value of unity,
 provided by the undeformed mirror, to a positive value greater than unity,
 e.g., 2.times., 3.times. or more. FIG. 8 illustrates in a general way the
 magnification variation of mirror 20 as a function of the pressure
 differential between plenum 36 and the atmosphere, which is in turn a
 function of flow cross-section reduction of throttle valve 64.
 When hydrostatic pressure within plenum 36 is reduced to a value
 approximating that of ambient atmospheric pressure, the elasticity of
 mirror diaphragm 30 restores it to a flat shape which provides unity
 magnification.
 Additional control of the hydrostatic pressure within plenum 36 and
 therefore of the magnification factor of mirror 20, may be obtained by
 varying the relative sizes of the inlet and outlet fluid-flow
 cross-sections of water flowing into and out of, respectively, plenum 36.
 Thus, the magnification of mirror 20 may be biased to have a value greater
 than unity even with throttle valve 64 fully open, by making the diameter
 of the outlet bore tubular fitting or outlet hose bore smaller than that
 of the inlet bore. Conversely, the magnification may be biased to have a
 smaller value even with throttle valve partially closed by making the
 maximum bore of the throttle valve and outlet port larger than that of the
 inlet port.