Patent Description:
Pressure gauges, such as inspection pressure gauges in fire suppression cylinders, are commonly used to indicate the pressure of fluids contained within pressure vessels. Such pressure gauges generally include a mechanical element coupling the pressurized fluid with a needle. Typically, when the mass of expellant within the fire suppression cylinder is sufficient to discharge suppressant contained within the fire suppression cylinder, the pressure of the expellant drives the needle to a location within the pressure gauge indicating that the fire suppression cylinder is ready for use. When the mass of expellant within the fire suppression cylinder is insufficient for use, such as when the fire suppression cylinder has been previously discharged or the fire suppression cylinder has leaked, the needle typically inhabits a location within the pressure gauge indicative that the fire suppression cylinder is not ready for use.

One challenge to using a pressure gauge to indicate readiness of a fire suppression cylinder is the effect of temperature on the expellant contained within the fire suppression cylinder. Specifically, because temperature of the expellant contained within the fire suppression cylinder can alter the expellant pressure, some pressure gauges can indicate low pressure when the fire suppression cylinder has neither leaked nor been discharged. To avoid unnecessary replacement or recharge due to temperature-induced pressure changes, technicians typically correct the displayed pressure for the ambient temperature when inspecting such cylinders; however, this introduces the risk that additional human error may be introduced into the inspection of fire suppression agent cylinders.

<CIT> discloses a pressure gauge using a compensating strip combined with, and having a different coefficient of expansion to, a Bourdon tube. <CIT> discloses a pressure gauge that similarly comprises a compensation element, in the form of a filler body within the Bourdon tube. Another known pressure gauge is disclosed in <CIT>.

Such systems and methods have generally been suitable for their intended purpose. However, there remains a need in the art for improved pressure gauges for fire suppression cylinders, and methods of measuring expellant pressure in fire suppression cylinders.

According to a first aspect, a pressure gauge is provided. The pressure gauge includes a housing having an inlet, a helical tube arranged within the housing with a closed end and an open end, the open end of the helical tube in fluid communication with the inlet, and a compensation member. The compensation member is arranged between the open end and the closed end of the helical tube, the compensation member fixed to the helical tube. The compensation member and the helical tube are formed from materials having different coefficients of thermal expansion to limit movement of the closed end of the helical tube due to temperature change of a compressed fluid in fluid communication with the helical tube. The compensation member is a bimetallic beam. The compensation member is connected along an entirety of the helical tube.

Optionally, the pressure gauge may include that the compensation member is directly connected to the helical tube.

Optionally, the pressure gauge may include that the compensation member is indirectly connected to the helical tube.

Optionally, the pressure gauge may include that the helical tube thermally couples the compensation member to the compressed fluid.

Optionally, the pressure gauge may include a compressed fluid including an expellant impounded within the helical tube.

Optionally, the pressure gauge may include that the open end of the helical tube is fixed relative to the housing, and that the free of the of the helical tube is free relative to the housing, and wherein the helical tube has an oblong profile.

Optionally, the pressure gauge may include a pointer fixed relative to the closed end of the helical tube, a scale underlying the pointer, and a window seated in the housing and overlying the pointer. The scale has an under-pressure segment coupled to an over-pressure segment by a ready segment.

Optionally, the pressure gauge may include that the helical tube is a bourdon tube.

According to a second aspect, a pressure vessel assembly is also provided. The pressure vessel assembly includes a pressure vessel defining a chamber and having a boss and a pressure gauge as described above seated in the boss and in fluid communication therethrough with the chamber of the pressure vessel. A compressed fluid including an expellant and a fire suppression material is contained with the chamber of the pressure vessel, a portion of the compressed fluid impounded within the helical tube.

Optionally, the pressure vessel assembly may include a pointer fixed relative to the closed end of the helical tube, a scale underlying the pointer, and a window seated in the housing and overlying the pointer. The scale has an under-pressure segment coupled to an over-pressure segment by a ready segment. The pointer remains fixed relative to the scale over a temperature range of between about between about -<NUM> degrees Celsius (about -<NUM> degrees Fahrenheit) and about <NUM> degrees Celsius (about <NUM> degrees Fahrenheit).

According to a third aspect, a method of making a pressure gauge is also provided. The method includes defining a housing having an inlet, arranging a helical tube within the housing with a closed end and an open end such that the open end of the helical tube is in fluid communication with the inlet, and arranging a compensation member arranged between the open end and the closed end of the helical tube such that the compensation member is fixed to the helical tube. The compensation member and the helical tube are formed from materials having different coefficients of thermal expansion to limit movement of the closed end of the helical tube due to temperature change of a compressed fluid in fluid communication with the helical tube. The compensation member is a bimetallic beam. The compensation member is connected along an entirety of the helical tube.

Technical effects of the present disclosure include compensation for temperature change differences in pressure of fluids contained within the pressure vessels. Technical effects also include limiting (or eliminating entirely) the need to manually compensate pressure displayed by a pressure gauge for ambient temperature of the fluid being measured by the pressure gauge.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a pressure gauge constructed in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments of pressure gauges, pressure vessel assemblies, and methods of displaying pressure within pressure vessel assemblies in accordance with the present disclosure, or aspects thereof, are provided in <FIG>, as will be described. The systems and methods described herein can be used for displaying temperature-compensated pressure within pressure vessels, such as in pressure gauges employed on fire suppression cylinders for leak detection, though the present disclosure is not limited to leak detection or to fire suppression cylinders in general.

Referring to <FIG>, a pressure vessel assembly <NUM>, e.g., a fire suppression cylinder, is shown. The pressure vessel assembly <NUM> includes the pressure gauge <NUM>, a pressure vessel <NUM>, a discharge valve <NUM>, and a compressed fluid <NUM>. The pressure vessel <NUM> has a wall <NUM> and a boss <NUM>. The wall <NUM> defines a chamber <NUM> within the pressure vessel <NUM>. The compressed fluid <NUM> is disposed within the chamber <NUM> and the discharge valve <NUM> is in fluid communication with the chamber <NUM> for selective coupling of the chamber <NUM> with the external environment <NUM>. The selective coupling of the chamber <NUM> to the discharge valve <NUM> allows for issue of the compressed fluid <NUM> therethrough to the external environment <NUM> upon actuation of the discharge valve <NUM>. In certain embodiments the compressed fluid <NUM> includes an expellant <NUM> and a fire suppression material <NUM>.

The pressure gauge <NUM> is seated on the boss <NUM> and is in fluid communication therethrough with the compressed fluid <NUM>. In this respect the pressure gauge <NUM> includes a housing <NUM>, a window <NUM>, and a scale <NUM>. The pressure gauge <NUM> also includes a pointer <NUM>, a helical tube <NUM>, a compensation member <NUM> (shown in <FIG>), and an inlet conduit <NUM>.

The housing <NUM> has an interior <NUM> (shown in <FIG>). The window <NUM> is seated in the housing <NUM> and is formed from a transparent material, such as glass or plastic. The scale <NUM> is supported within the housing <NUM> and is fixed relative to the housing <NUM>. The pointer <NUM> is movably supported within the interior <NUM> of the housing <NUM> and is registered to the scale <NUM> according to pressure of the compressed fluid <NUM>. As shown in <FIG>, the scale <NUM> has an under-pressure segment <NUM> coupled to an over-pressure segment <NUM> by a ready segment <NUM>. As will be appreciated by those of skill in the art in view of the present disclosure, pressure gauges having other types of scales can also benefit from the present disclosure, such as pressure gauges having graduated scales and colored indicators by way of non-limiting example.

With reference to <FIG>, the pressure gauge <NUM> is shown. The housing <NUM> has an inlet <NUM> defined by the inlet conduit <NUM>. The inlet <NUM> is in fluid communication with the chamber <NUM> (show in <FIG>) for communication of pressure of the compressed fluid <NUM>, and in certain embodiments the compressed fluid <NUM>, to the pressure gauge <NUM>. The inlet conduit <NUM> in turn extends into the interior <NUM> of the housing <NUM> and is in fluid communication with the helical tube <NUM>.

The helical tube <NUM> has an open end <NUM> and a closed end <NUM> and is formed from a helical tube material <NUM> (shown in <FIG>). The open end <NUM> of the helical tube <NUM> is fixed relative to the housing <NUM> and is connected to the inlet conduit <NUM>. The closed end <NUM> is free relative to the housing <NUM> and is fixed thereto the pointer <NUM>. Between the open end <NUM> and the closed end <NUM> the helical tube <NUM> the helical tube <NUM> defines an oblong profile <NUM> (shown in <FIG>). In certain embodiments the helical tube <NUM> can be a bourdon tube.

The pointer <NUM> is fixed to the closed end <NUM> of the helical tube <NUM> and is movable therewith according to pressure of the compressed fluid <NUM> communicated to the open end <NUM> of the helical tube <NUM>. In this respect the pointer <NUM> is registered relative to the scale <NUM> according to pressure of the compressed fluid <NUM> communicated to the open end <NUM> of the helical tube <NUM>. As shown in <FIG> the pointer <NUM> overlays the scale <NUM> and the window <NUM> overlays the pointer <NUM>, the pointer <NUM> arranged between the scale <NUM> and the window <NUM>.

With reference to <FIG>, a portion of the pressure gauge <NUM> is shown. As will be appreciated by those skill in the art in view of the present disclosure, registration of the pointer <NUM> to the scale <NUM> generally provides an indication of the mass of the compressed fluid <NUM> contained within the chamber <NUM> (shown in <FIG>) of the pressure vessel <NUM> (shown in <FIG>). For example, the pressure gauge <NUM> can be configured such that the pressure of the compressed fluid <NUM> communicated to the helical tube <NUM> for a predetermined mass of the compressed fluid <NUM> at a predetermined nominal temperature register the pointer <NUM> to the ready segment <NUM> of the scale <NUM>, the pressure gauge <NUM> thereby providing a ready-to-use indication <NUM>.

As will also be appreciated by those of skill in the art in view of the present disclosure, pressure of the compressed fluid <NUM> (shown in <FIG>) communicated to the helical tube <NUM> can change with temperature of the compressed fluid <NUM>. In some pressure vessel assemblies such temperature-induced pressure change can displace the pointer <NUM> from the ready segment <NUM> of the scale <NUM>. For example, when sufficiently cool (relative to a nominal temperature), the pressure communicated by the compressed fluid <NUM> to the helical tube <NUM> can displace the pointer <NUM> such that the pointer <NUM> becomes registered to the under-pressure segment <NUM> of the scale <NUM> - the pressure gauge <NUM> potentially providing an under-pressure indication <NUM> (shown with dashed pointer outline) that the pressure vessel assembly <NUM> has developed a leak and is therefore unserviceable when the pressure vessel assembly <NUM> is in fact ready-to-use. Oppositely, when sufficiently warm (relative to the nominal temperature), the pressure communicated to the helical tube <NUM> can displace the pointer <NUM> such that the pointer <NUM> becomes registered to the over-pressure segment <NUM> of the scale <NUM> - the pressure gauge <NUM> potentially providing an over-pressure indication <NUM> (also shown with dashed pointer outline) that the pressure vessel assembly <NUM> is overcharged when the pressure vessel assembly <NUM> is in fact properly charged. To limit (or eliminate entirely) the presentation of the under-pressure indication <NUM> and the over-pressure indication <NUM> when the pressure vessel <NUM> in fact contains the proper mass of compressed fluid <NUM>, e.g., the expellant <NUM> (shown in <FIG>), the pressure gauge <NUM> includes the compensation member <NUM>.

With reference to <FIG>, portions of the helical tube <NUM> and the compensation member <NUM> are shown. The helical tube <NUM> impounds within its interior a portion of the compressed fluid <NUM> between the open end <NUM> (shown in <FIG>) and the closed end <NUM> (shown in <FIG>) of the helical tube <NUM> and is formed by the helical tube material <NUM>. The compensation member <NUM> is fixed to the helical tube <NUM> between the open end <NUM> and the closed end <NUM> of the helical tube <NUM> such that the helical tube <NUM> thermally couples the compressed fluid <NUM> to the compensation member <NUM> and is formed from a compensation member material <NUM>. The compensation member material <NUM> is different than the helical tube material <NUM>. More specifically, the helical tube material <NUM> has a coefficient of thermal expansion <NUM> that is different than a coefficient of thermal expansion <NUM> of the compensation member material <NUM>.

In an example not forming part of the claimed invention, the compensation member material <NUM> and the helical tube material <NUM> can both be metallic materials, the helical tube <NUM> and the compensation member <NUM> thereby defining a bimetallic beam <NUM> containing the compressed fluid <NUM>. It is contemplated that the coefficient of thermal expansion <NUM> of the compensation member material <NUM> be such that compensation member <NUM> opposes (and in certain embodiments prevents entirely) movement of the closed end <NUM> (shown in <FIG>) of the helical tube <NUM> due to change in temperature of the compressed fluid <NUM>, e.g., via communication of heat H between the compensation member <NUM> and the compressed fluid <NUM> through the helical tube <NUM>. Examples of suitable helical tube materials include stainless steel, brass, and bronze materials. Examples of suitable compensation member materials include stainless steel, brass, bronze, and/or aluminum materials differing in composition from that of the helical tube material <NUM>.

In certain embodiments the compensation member <NUM> can be directly connected to the helical tube <NUM>, such as through a deposition technique. Direct connection of the compensation member <NUM> to the helical tube <NUM> limits thermal resistance between the compressed fluid <NUM> and the compensation member <NUM>, limiting delay in response of the compensation member <NUM> to temperature change of the helical tube <NUM>. In accordance with certain embodiments the compensation member <NUM> can be indirectly connected to the helical tube <NUM>, such as by a braze or weld <NUM>. Indirect connection of the compensation member <NUM> to the helical tube <NUM> can simplify the manufacture of the pressure gauge <NUM>.

With continuing reference to <FIG>, the compensation member <NUM> is connected to the helical tube <NUM> along substantially the entirety of the helical tube <NUM>, e.g., being conformally disposed thereon or connected thereto by the braze or weld <NUM> (shown in <FIG>). Connecting the helical tube <NUM> along substantially the entirety of the helical tube <NUM> (i.e. the entire length of the helical tube) provides a relative uniform balancing to the offsetting contraction and expansion of the helical tube <NUM> and the compensation member <NUM> in response to a change of the compressed fluid <NUM> along the helical tube, limiting strain with the helical tube.

With reference to <FIG>, <FIG>, and <FIG>, cooperation of the compensation member <NUM> and the helical tube <NUM> is shown. As shown in <FIG>, once the pressure vessel <NUM> is charged pressure of the compressed fluid <NUM> is communicated to the helical tube <NUM> by the inlet conduit <NUM> (shown in <FIG>). Since the helical tube <NUM> is closed on one end the pressure of the compressed fluid <NUM> is operative to displace the closed end <NUM> of the helical tube <NUM> according to magnitude of the pressure of the compressed fluid <NUM>. At nominal temperature and nominal mass of the compressed fluid <NUM> the pressure causes the helical tube <NUM> to position the pointer <NUM> along the ready segment <NUM> of the scale <NUM>.

As shown in <FIG>, decrease in pressure of the compressed fluid <NUM>, e.g., from a decrease in the mass of compressed fluid <NUM> due to actuation of the discharge valve <NUM> (shown in <FIG>) or leakage from the pressure vessel <NUM> (shown in <FIG>), exerts a deformation force <NUM> on the helical tube <NUM>. The deformation force <NUM> urges the helical tube <NUM> to become more tightly wound according to the magnitude of the deformation force <NUM>, diameter of the turns of the helical tube <NUM> tending to decrease. The resulting deformation displaces the closed end <NUM> of the helical tube <NUM>, and thereby the pointer <NUM>, toward the under-pressure segment <NUM> of the scale <NUM>. At nominal temperature the pressure gauge <NUM> indicates the decrease in the mass of the compressed fluid <NUM> contained within the pressure vessel <NUM> with deflection <NUM> of the pointer <NUM> relative to the scale <NUM> in the direction of the under-pressure indication <NUM> (shown in <FIG>).

When temperature decrease of the compressed fluid <NUM> is responsible for the pressure decrease, the compensation member <NUM> exerts a deformation compensation force <NUM> in opposition to the deformation force <NUM>. Specifically, as temperature of the compensation member <NUM> and the helical tube <NUM> decreases the compensation member material <NUM> (shown in <FIG>) forming the compensation member <NUM> contracts more slowly than the helical tube material <NUM> (shown in <FIG>) forming the helical tube <NUM>. The slower rate of contraction of the compensation member material <NUM> relative to that of the helical tube material <NUM> causes the compensation member <NUM> to exert the deformation compensation force <NUM> on the helical tube <NUM>. The deformation compensation force <NUM> is exerted in a direction opposite that of the deformation force <NUM>, the deformation compensation force <NUM> thereby limiting movement of the closed end <NUM> of the helical tube <NUM>. Consequently, the pointer <NUM> remains in registration with the ready segment <NUM> of the scale <NUM> and does not move into registration with the under-pressure segment <NUM> of the scale <NUM>, as would otherwise occur in response to the temperature decrease.

In certain embodiments the closed end <NUM> exhibits substantially no movement due to pressure change within the pressure vessel <NUM> due to temperature change within a range of about -<NUM> degrees Celsius (about -<NUM> degrees Fahrenheit) and about <NUM> degrees Celsius (about <NUM> degrees Fahrenheit). Absence of movement within this range can prevent temperature changes within a range commonly experienced by fire suppression cylinders from displaying a decrease in mass of the compressed fluid <NUM> contained within the pressure vessel <NUM> when, in fact, the mass of the compressed fluid <NUM> contained within the pressure vessel <NUM> (shown in <FIG>) is unchanged.

As shown in <FIG>, increase in pressure of the compressed fluid <NUM>, such as due to an addition to the mass of the compressed fluid <NUM> contained within the pressure vessel <NUM> (shown in <FIG>), exerts a deformation force <NUM> on the helical tube <NUM>. The deformation force <NUM> urges the helical tube <NUM> to become less tightly wound according to the magnitude of the deformation force <NUM>. At nominal temperature the resulting deformation of the helical tube <NUM> displaces <NUM> the closed end <NUM> of the helical tube <NUM>, and thereby the pointer <NUM>, toward the over-pressure segment <NUM> of the scale <NUM>. The pressure gauge <NUM> thereby indicates an increase in the mass of the compressed fluid <NUM> contained within the pressure vessel <NUM> with registration of the pointer <NUM> along the over-pressure segment <NUM> of the scale <NUM>.

When the pressure change within the pressure vessel <NUM> (shown in <FIG>) is due to temperature increase of the compressed fluid <NUM>, the compensation member <NUM> exerts a deformation compensation force <NUM> in opposition to the deformation force <NUM>. Specifically, as temperature of the compressed fluid <NUM> increases, the compensation member material <NUM> (shown in <FIG>) forming the compensation member <NUM> expands at a rate different than that of the helical tube material <NUM> (shown in <FIG>) forming the helical tube <NUM> in response to the temperature increase. The different rates of expansion in response to the temperature increase causes the compensation member <NUM> to exert the deformation compensation force <NUM> on the helical tube <NUM> in a direction opposite the deformation force <NUM>, also limiting movement of the closed end <NUM> of the helical tube <NUM>. Consequently, the pointer <NUM> remains in registration with the ready segment <NUM> of the scale <NUM> and does not move into registration with the over-pressure segment <NUM> of the scale <NUM>, as would otherwise occur due to the temperature increase.

In certain embodiments the closed end <NUM> exhibits substantially no movement due to pressure change within the pressure vessel <NUM> due to temperature change within a range of about -<NUM> degrees Celsius (about -<NUM> degrees Fahrenheit) and about <NUM> degrees Celsius (about <NUM> degrees Fahrenheit). As above, absence of movement within this range can prevent temperature changes within a range commonly experienced by fire suppression cylinders from displaying an increase in mass of the compressed fluid <NUM> contained within the pressure vessel <NUM> when no mass has been added to the chamber <NUM> (shown in <FIG>) of the pressure vessel <NUM> (shown in <FIG>).

Pressure gauges can be employed on fire suppression cylinders to provide indication of pressure within the fire suppression cylinder, such as due to actuation of the fire suppression cylinder and/or leakage from the fire suppression cylinder. In some fire suppression cylinders the pressure displayed by a pressure gauge can be influenced by factors other than actuation and/or leakage, such as pressure change due to temperature change of the fire suppression cylinder. In such event a fire suppression cylinder that is otherwise ready for use can appear to be in either an under-pressure or over-pressure condition. This can result in unnecessary service and/or replacement of the fire suppression cylinder.

In embodiments described herein pressure gauges with compensation members are employed to understate or overstate pressure reported by pressure gauges when pressure change within the fire suppression cylinder is due to change in temperature relative to a nominal temperature. In certain embodiments the compensation member is directly connected to helical tube, e.g., between an open end and a closed end of a helical tube, the compensation member and the helical tube thereby cooperating as a bimetallic beam. In accordance with certain embodiments the material forming the compensation member and the shape of the compensation member are selected such that the closed end of the helical tube does not move in response to temperature-driven temperature changes within a range of between about -<NUM> degrees Celsius (about -<NUM> degrees Fahrenheit) and about <NUM> degrees Celsius (about <NUM> degrees Fahrenheit), the compensation member thereby preventing temperature change a fire suppression from suggesting that the fire suppression cylinder has been overfilled, actuated and/or leaked.

Claim 1:
A pressure gauge (<NUM>), comprising:
a housing (<NUM>) having an inlet (<NUM>);
a helical tube (<NUM>) arranged within the housing with a closed end (<NUM>) and an open end (<NUM>), the open end of the helical tube in fluid communication with the inlet; and
a compensation member (<NUM>) arranged between the open end and the closed end of the helical tube, the compensation member fixed to the helical tube,
wherein the compensation member and the helical tube (<NUM>) are formed from materials (<NUM>, <NUM>) having different coefficients of thermal expansion (<NUM>, <NUM>) to limit movement of the closed end (<NUM>) of the helical tube due to temperature change of a compressed fluid (<NUM>) in fluid communication with the helical tube; and
the compensation member (<NUM>) is a bimetallic beam
characterised in that:
the compensation member (<NUM>) is connected to the helical tube (<NUM>) along an entirety of the helical tube (<NUM>).