GB2113770A

GB2113770A - Device for summating pressures

Info

Publication number: GB2113770A
Application number: GB08301966A
Authority: GB
Inventors: Arthur Lewis Dimond
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-01-28
Filing date: 1983-01-25
Publication date: 1983-08-10
Also published as: GB2113770B; GB8301966D0

Abstract

Fluid pressures in a plurality of (e.g.) load cells are communicated to respective input cylinders 24, 26, 28, 30 containing respective input pistons 40, 42, 44, 46. These pistons are all integral parts of a composite piston 20, which also provides a single output piston in an output cylinder 18 which is opposed to the input cylinders 24-30. Thus the output cylinder 18 experiences an output pressure which depends on the pressures in all of the input cylinders 24-30, which will generally all be of the same area so as to contribute equally to the output pressure. The input cylinders and pistons may all be concentric, so that all bar the central ones (24, 40) are annular. The piston has rubber seals 48, 50, 52. <IMAGE>

Description

SPECIFICATION Device for summating pressures This invention relates to the field of pressure measurement. It is particularly useful in systems in which two or more load cells support a load, each producing a hydraulic pressure depending on the load, which can be measured in order to measure the load.

It is known to support a load on a load cell having a hydraulic output line. The pressure depends directly on the weight of the load, and so if the output line is taken to a Bourdon or other pressure gauge the load can be measured. An improved load cell is shown in my application 8202440.

HYDRAULIC PISTON AND CYLINDER ASSEMBLY In practice, load cells are used under load platforms, hoppers etc., which require three or four support points, and thus three or four load cells are needed. To give an accurate indication of the load, a specially designed Bourdon gauge is used, in which the required number of hydraulic inputs act on a single indicator bar, so that the indication given relates to the mean or the sum of the input pressures.

The accuracy of such an arrangement suffers, however, because of mechanical problems in ensuring that all the inputs act in an identical manner on the indicator bar.

The present invention provides a device for producing an output pressure representative of a plurality of input pressures, comprising a composite piston slidable on one side in an output cylinder, and in opposition thereto having a plurality of input piston members which are slidable in respective input cylinders, whereby fluid pressure in the respective input cylinders is transmitted to fluid in the output cylinder to give an output fluid pressure representative of the input pressures.

It will be appreciated that the term "cylinder" is used to denote the function of the element concerned, rather than its cross-sectional shape. In fact, in a preferred form, all but one of the input cylinders are annular, with the input cylinders and their correspondingly shaped input piston members being arranged concentrically. This may give a better balance to the piston under differing input pressures, improving accuracy. Preferably, the input piston members and input cylinders should each have the same cross-sectional area.

An embodiment of the invention will now be described by way of example, with reference to the accompanying drawing, which is a cross-section through the device.

Referring to the drawing, the outer casing is machined in two mating cylindrical parts 10, 1 2. The casing part 10 has an annular spigot 14 around the periphery of the mating face 1 5, which engages a corresponding recess in the casing part 1 2 to ensure accurate fitting. The two parts are held together in use by three or four bolts 16, only one of which is seen in the drawing.

The interior of the casing part 10 is machined with an output cylinder 1 8, which receives a piston 20. An output port 22 leads from the cylinder 18, and can be provided with internal threading for connection of a capillary tube leading to a standard Bourdon or other pressure gauge.

The mating face 1 5 of the casing part 12 is machined with a central cylindrical recess 24, and with three annular grooves 26, 28, 30. These provide four concentric input cylinders, and they are provided with respective inlet ports 32, 34, 36, 38. The inlet ports may also have internal threading for connection of capillary tubes.

The outer cylindrical surface of the piston 20 is machined to fit with a close tolerance in the cylinder 18. The face of the piston which faces the casing part 12 is machined with three grooves, defining one cylindrical piston member 40 and three concentric annular piston members 42, 44, 46.

These fit with a close tolerance in the respective cylinders 24, 26, 28, 30.

The cylinder 1 8 contains a rubber sealing disc 48 flush against the face of the piston 20. When the system is under pressure, this is compressed and seals radially against the cylinder walls. Thus hydraulic fluid in the cylinder 18 cannot flow past the piston. Similarly, the input cylinders 24, 26, 25, 30 have a rubber sealing disc 50 or annular rubber seals 52 as appropriate, which seal them in exactly the same manner. The principle of these seals is similar to that described in my application 8202440 mentioned above.

The four input cylinders 24, 26, 28, 30 all have the same cross-sectional area, and of course the piston members 40, 42, 44, 46 therefore also have the same cross-sectional areas. To achieve this, the inner and outer diameters of the cylinders are as shown in Table 1.

TABLE 1 Inner diameter (inches) Outer diameter (inches) Cylinder (centimetres in brackets) (centimetres in brackets) 24 1.596 (4.054) 26 2.096 (5.324) 2.634 (6.690) 28 3.134 (7.960) 3.517 (8.933) 30 4.017 (10.203) 4.322 (10.978) If other cylinder arrangements are required, the calculations to give equal cross-sectional areas are of course very simple. The use of equal cross-sectional areas is important unless one or more of the input pressures is to be "weighted" with respect to the others.

In use, the inlet ports 32, 34, 36, 38 are connected to load cells under a load to be measured. The hydraulic pressures from the load cells are transmitted to the cylinders 24, 26, 28, 30 and act on the piston members 40, 42,44, 46. The piston 20 then transmits to the fluid in the output cylinder 18 a composite pressure proportional to the sum or the mean of the input pressures. This is measured on the standard Bourdon gauge, which may be calibrated directly in terms of the weight of the load being measured.

When filling the system with hydraulic fluid, use is made of a sight hole 54 in the casing part 10.

The cylinder 18 and the tube to the Bourdon gauge are filled with fluid, and the piston 20 is displaced to the left (as seen in Fig. 1). Fluid is now charged into the load cells and through the connecting tubing to the input cylinders, and the casing parts 10, 12 are bolted firmly together. Now further fluid is charged into the output tube, pushing the piston 20 to the right and pushing fluid from the input cylinders back through the load cells, until a groove 56 is seen to be central in the sight hole 54. The various filling ports in the output to the Bourdon gauge and the load cells are now closed, and the system is ready for use.

Claims

1. A device for producing an output pressure representative of a plurality of input pressures, comprising a composite piston slidable on one side in an output cylinder, and in opposition thereto having a plurality of input piston members which are slidable in respective input cylinders, whereby fluid pressure in the respective input cylinders is transmitted to fluid in the output cylinder to give an output fluid pressure representative of the input pressures.

2. A device according to claim 1 wherein the composite piston is of unitary construction, having at the input side a plurality of concentric annular grooves so that upstanding portions are defined between them to provide said input piston portions.

2. A device according to claim 1 wherein the composite piston has at the input side a plurality of concentric annular grooves so that upstanding portions are defined between them, said upstanding portions constituting said input piston members.

3. A device according to claim 1 or claim 2 wherein all of the input cylinders are of equal cross sectional area.

4. A device according to any preceding claim wherein one or more of the input and output cylinders contains a respective rubber seal constructed and arranged so that pressure in the cylinder urges it to seal radially against the cylinder wall or walls so as to restrain the passage of fluid in the cylinder past the piston.

5. A device according to any preceding claim wherein the output and input cylinders are provided by output and input parts of a housing, which parts are secured together so as to enclose the composite piston.

6. A device according to claim 5 wherein the input part of the housing provides inlet ports for the input cylinders; and the output part provides an outlet port for communicating the output cylinder to a pressure gauge.

7. A device for producing an output pressure representative of a plurality of input pressures substantially as described herein with reference to the accompanying drawing.

New claims or amendments to claims filed on 27 April 1 983.

Superseded claims 1 and 2.

New or amended claims:

1. A device for producing an output pressure representative of a plurality of input pressures, comprising a composite piston slidable on one side in an output cylinder, and in opposition thereto having a compound input piston having a plurality of concentric input piston portions which are slidable in respective concentric input cylinders, whereby in use the input pressure in each input cylinder is transmitted to fluid in the output cylinder to give an output fluid pressure representative of the input pressures.