GB2311860A

GB2311860A - Differential pressure gauge with adjustable scale

Info

Publication number: GB2311860A
Application number: GB9700080A
Authority: GB
Inventors: Eric William Absolon
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-01-03
Filing date: 1997-01-03
Publication date: 1997-10-08
Anticipated expiration: 2017-01-03
Also published as: GB2311860B; GB9700080D0

Abstract

A differential pressure gauge with either manually or automatically adjustable scale 11 as a function of flow rate, such that a scale is presented at, for example, any given flow rate or other variable parameter, enabling the gauge to show the differential pressure that would have existed at an alternative maximum flow rate or other variable, for example a filter rated flow. The means for adjusting the scale includes a flow sensing device 15 coupled to an adjustable scale control 16.

Description

INPROVEMENTS IN OR RELATING TO DIFFERENTIAL PRESSURE HEASUREMENT This invention relates to devices used to monitor the condition of filters in fluid flow circuits.

Devices used to monitor the condition of filters in a fluid flow circuit typically consist of a differential pressure gauge used to measure the pressure drop, or flow resistance, across the filter elements. As the filter element progressively becomes blocked with retained contaminants, the pressure drop across the element increases and thus a differential pressure gauge is a measure of the degree of contanination. But the pressure drop across the elenent is also a function of other variable parameters such as the rate of flow or the viscosity of the fluid passing through the element and thus, the pressure drop is only an indication of the element contamination state at, as an example used throughout this specification, a given rate of flow.

Therefore the gauge reading at the actual rate of flow pertaining could be lower or higher than the reading at the defined filter rated flow and therefore misleading and unreliable as an indication of element condition.

Devices are known that seek to modify the reading of a differential pressure gauge as a function of rate of flow such that the gauge gives a reading equivalent to the reading that would exist at a defined maximum, or, filter rated flow rate. The disadvantage of such devices is that they are complicated and, by their nature, only an approximation of the actual filter characteristics, which can vary from filter to filter depending on the nature of the element and it's embodiment within the filter casing and can vary between a square law and a linear relationship of flow to pressure drop. As such, a device of the known nature can only be an approximation and, without internal modification, applicable to only one type of filter.

A further disadvantage is that only the modified reading can be obtained, the actual differential pressure existing at the particular flow rate is not available.

A further disadvantage is that only rate of flow as a variable can be taken into account.

The object of the present invention is to provide a simple method of adjusting the scale of a conventional differential pressure gauge as a function of flow rate, or any other variable parameter, such that the adjustment represents exactly the the nature of the individual filter characteristic. The adjustment of the scale can be by manual means if the flow rate is known, or automatically by a flow sensor if flow rate is not known. A feature of the invention is that the individual filter characteristic is embodied on a chart incorporated in the device which represents, graphically, the actual filter pressure drop flow curves for different levels of contamination and which can readily be changed without internal modification of the device.

A further feature is that the basic differential pressure gauge remains unmodified and presents a scale of actual differential pressure at the particular fow rate as well as the scale adjusted to show the value of differential pressure that would exist at filter rated flow. This is an important operational feature.

A specific embodiment of the invention will now be described,by way of an example, with reference to the accompanying drawings Figure 1 depicts a differential pressure gauge of a form commonly used. In the embodiment of the invention described, a scale is attached that can be rotated as a function of rate of flow and thereby present a scale reading converted to that which would exist at the filter maximum rated flow.

Figure 2 depicts an example of the adjustable scale in the form of a chart.

A typical known differential pressure gauge consists of a body 1 containing a piston 2 in a glass tube 3 supported hy a spring 4 such that deflection of the piston is proportional to differential pressure across a filter 5 sensed by port 6 connected to filter upstream and port 7 connected to filter downstream. In this invention, attached to the body 1 is a housing 8 containing a rotatable drum 9 operated by a control 10. The drum has a chart 11 wrapped around it and protected by a transparant cover 12 nounted in such a wav that the top of the piston 2 can be aligned with the chart 11 to obtain a reading. On the other side of the gauge body 1 a fixed scale 13 is mounted which can also be read at the top of the piston. The chart 11 on the rotatable drum 9 also carries a scale of percentage of filter maximum rated flow or, if required, figures of actual flow for a given filter installation. The drum 9 is rotated by control 10 until the percentage of rated flow, or actual flow, pertaining at the time is shown in window 14. The rotatable scale on chart 11 then shows differential pressure corrected to filter rated flow and the alternative fixed scale 13 shows the uncorrected differential pressure, that is the differential pressure that would have been shown by a conventional differential pressure gauge without flow correction.

Fig. 1 is drawn to show a corrected differential pressure of 1 kg/cma at a flow rate equal to 70S of filter rated flow, whilst the actual diferential pressure shown on the conventional scale 13 is only 6 kg/cm2 The control 10 could be manually operated in the simplest form of the device and where the actual rate of flow is known, but could also be autonatically operated by a flow sensing device 15 mounted in the pipe line containing the filter and which could be an orifice plate, a venturi, pitot head or any other known flow sensing device, connected to an actuator 16 attached to or replacing control 10.

A typical automatic system could be an orifice plate 15 sensing, as a result of flow rate, differential pressure and applying to a vane type actuator 16 with a rotating vane 17 restrained by a torsion spring 1S, such that rotation of the vane and therefore drum 9 is a function of flow rate. Non-linearities of such a system are easily eliminated by modifying the the flow scale of chart 11 accordingly. It will be understood that the flow detection system described is typical of several different methods that could be employed and which do not affect the basic invention.

Fig. 2 shows a typical chart 11 as prepared prior to wrapping round the drum 9, the length of the chart being equal to the drum circumference. The lower axis 19 of the chart is graduated in terms of percentage of filter maximum rated flow, typically but not necessarily from 100% to 40% as a practical range. Alternatively, the graduation could be in actual flow rate units to suit the filter being monitored. The left hand vertical scale 20 at 100% represents the known differential pressure across the filter at varying degrees of filter element contamination, the actual values indicated by the numbers marked alongside each curve on the chart such that they are visible at any rotary position of the drum 9. The curves are such that for each level of contamination they.

represent the pressure drop/flow characteristics of the particular filter being monitored.

The chart could have features added, for example a heavy line 21 representing the maximum level of contamination acceptable and at which filter element should be changed.

Another feature could be the colouring of the sector above line 21 green as being the safe sector and the sector below line 21 red indicating an unsafe operational area and the need to change the filter elements.

Claims

1. A differential pressure gauge, such as that used to monitor the flow resistance through a device in a flowing stream, with a scale attached that is adjustable as a function of a variable parameter such as flow rate or viscosity such that the scale reads differential pressure that would exist at, for example, a defined rated flow of the device in the stream.

2. A differential pressure gauge according to Claim 1 also retaining a non-adjustable scale in addition to the adjustable scale, such that readings of actual differential pressure at a given flow rate are obtainable simultaneously with a reading adjusted to rated flow of the device in the stream.

3. A differential pressure gauge according to Claim 2 wherein the adjustable scale is incorporated as a drum rotatable as a function of flow rate.

4. A differential pressure gauge according to Claim 3 wherein the adjustable scale is in the form of a chart wrapped around the rotatable drum.

5. A differential pressure gauge according to Claim 4 wherein the chart wrapped around the rotatable drum is protected by a removable transparant cover such that the chart is readily exchanged.

6. A differential pressure gauge according to claim 5 wherein the rotatable drum is manually rotated to correspond with a known flow rate.

7. A differential pressure gauge according to Claim 6 wherein the rotatable drum is rotated automatically by a flow sensing device.

8. A differential pressure gauge according to any preceding claim used to monitor the condition of a filter element.

9. A differential pressure gauge for monitoring the resistance through a flow device substantially as described herein with reference to accompanying drawings Figure 1 and Figure 2.

10. A differential gauge including devices according to any preceding claim.