GB2244096A - Pulsation damper - Google Patents

Abstract

A pulsation damper for reducing pulsations in gas flowing along a line comprises a tubular body (10) having input and output ports (12, 14). An open-ended Neoprene tube (16) extends within the body, with the ends of the tube being wrapped back over the body and held there by press fit end caps (18, 20). Gas flowing between the inlet port (12) and the outlet port (14) is damped by virtue of the flexibility of the Neoprene tube (16). To allow for pressure equalisation within the damper, the end caps are provided with apertures (30, 32). <IMAGE>

Description

PULSATION DAMPER The present invention relates to pulsation dampers, and particularly although not exclusively to such a damper for use in gas detection apparatus incorporating an electrochemical sensor.

In conventional gas detection apparatus, air to be tested for the presence of a particular gas is supplied to an electrochemical sensor via an input line. The air is forced along this line by a pump of some sort, typically a diaphragm pump driven by means of an electric motor.

The repeating action of the pump, for example the back and forth movement of the diaphragm of a diaphragm pump, causes pressure fluctuations or pulses within the input line, these pulses eventually reaching the sensor itself. It has been found in practice that the effect of a typical pulsation frequency of about 800 cycles per second affects to some degree the operation of the sensor and causes it to overestimate slightly the amount of the gas present that it is detecting. One could, of course, easily compensate if the affect were constant, but in practice where the pump is being driven by an electric motor from a battery, the gradual running down of the battery changes the repeating frequency of the pump and thus the frequency of the pulses. This in turn is likely to change the sensor output error.

It is a first object of the present invention at least to alleviate the above problems.

To that end, the present applicants have designed a suitable pulsation damper to be inserted into the input line, so that the air is applied to the electrochemical sensor at a more constant pressure over the testing period.

It is a further object of the invention to provide a cheap and convenient pulsation damper for use in other applications.

According to the present invention there is provided a pulsation damper comprising an open-ended tubular body having input and output ports therein and a flexible open-ended tube within the body, the ends of the tube being secured to the body thereby defining a closed flow path from the input port, between the body and the tube, to the output port.

The fact that at least one of the tubular body and one end of the flexible tubes is open ensures that there is not too great a pressure differential across the flexible tube when the pressure applied to the input port is a little over atmospheric. Conveniently, both ends of the body and of the tube are open. In this case, the periphery of each open end of the tube may be secured to the corresponding open periphery of each end of the body, for example by folding the tube ends over the ends of the body. The pulsation damper may be provided with one or more separate end caps for securement to the ends of the body, so protecting the flexible tube inside.Of course, if such caps are provided, at least one of them should have an aperture in it to allow the ambient pressure to be applied to the inner surface of the flexible tube, that is the surface opposite to that which is in contact with the line pressure.

In a preferred embodiment, each end cap is a close fit over a respective end of the body, one end of the flexible tube being trapped between each cap and the body. To assist in retention of the end, a circumferential bead on the body may be arranged to mate within a corresponding circumferential groove in the cap, with the end of the tube being trapped between the two. Alternatively, there could be a groove in# the body and a bead on the cap. Another alternative, rather less preferred, would be to arrange for the cap to fit within the periphery of the end of the body, with the end of the flexible tube then being trapped between the outer periphery of the cap and the inner periphery of the body.

The tubular body may, but need not, be circular in cross section. The flexible tube, likewise, conveniently has a circular section.

The invention may be carried into practice in a number of ways and one specific embodiment will now be described, by way of example, with reference to the drawing which shows an exploded cross-sectional view of a pulsation damper embodying the present invention.

The damper comprises an open-ended circular-section tubular body 10, conveniently of metal or of a plastics material. Towards one end of the body there is an input port 12, and towards the other end, on the far side, an output port 14. Within the body 10 is an open-ended flexible Neoprene tube 16, the ends of which are stretched over the ends of the body and folded back.

The ends of the neoprene tube are held in position by two end caps 18, 20 which are a push fit over the ends of the body. Circumferential beads 22, 24 at the ends of the body are received within respective circumferential grooves 26, 28 in the caps.

In use, an airflow having pulsations that are to be damped is supplied to the inlet port 12. The air makes its way via the annular space 40 between the flexible tube 16 and the body 10 to the outlet port 14. The fluctuations are damped by virtue of movement of the tube 16. Where the device is to be used at a pressure slightly higher than atmospheric, the inner volume 50 of the tube 16 should be vented to atmosphere, and to that end there are provided apertures 30, 32 in the end caps 18, 20.

It has been found in practice that a Neoprene tube about 7cm long and 2cm in diameter, located within a body 4cm long and 2cm in diameter provides substantial damping of the pulsations provided by a typical diaphragm pump, believed to operate at about 800 pulses per second. The tuning is, however, not particularly critical and the present pulsation damper is effective over a relatively broad frequency band. This makes it useful in reducing fluctuations in a system where the frequency is likely to alter with time, for example due to the running down of a battery driving an electric pump. The frequency is also likely to vary with the amount of wear on the pump, and thus with its age.

The frequency band can be changed by altering the length of the body and the Neoprene tube.

Claims (11)

CLAIMS:

1. A pulsation damper comprising an open ended tubular body having input and output ports therein and a flexible open-ended tube within the body, the ends of the tube being secured to the body thereby defining a closed flow path from the inlet port, between the body and the tube, to the outlet port.

2. A pulsation damper as claimed in claim 1 in which both ends of the flexible tube and of the tubular body are open.

3. A pulsation damper as claimed in claim 2 in which the ends of the tube are secured, around their peripheries, to the respective ends of the body.

4. A pulsation damper as claimed in claim 3 in which the ends of the tube are folded back over the respective ends of the body.

5. A pulsation damper as claimed in any one of the preceding claims in which the or each open end of the body has a protective apertured end cap.

6. A pulsation damper as claimed in claim 5 in which the or each end cap secures an end of the flexible tube to the respective end of the body.

7. A pulsation damper as claimed in claim 6 in which the or each end cap is a press fit over the respective end of the body, the cap being retained by the interaction of a bead and groove.

8. A gas detector comprising an air input line, a pump for drawing air along the input line and for supplying it to a sensor, and a pulsation damper, as claimed in any one of the preceding claims, in the input line.

9. A gas detector as claimed in claim 8 in which the sensor is of the electrochemical type.

10. A gas detector as claimed in claim 8 or claim 9 being a hand-held unit, the pump being driven by an electric motor powered by a battery.

11. A pulsation damper substantially as specifically described with reference to the drawing.