Personal Air Sampling Pump

Abstract

A lightweight, portable air pump employing a solenoid driven rubber diaphragm and rubber flapper check valves to control inlet and outlet flow. The diaphragm has a flexible annulus and a rigid central section so that there is virtually no accommodation to load, used with independently timed drive pulses for essentially constant flow with varying load.

Description

BACKGROUND OF THE INVENTION

The invention described herein was made in the course of employment by the U. S. Atomic Energy Commission.

The airborne contaminants a worker breathes, especially in mines and similarly confined locations, are the subject of growing concern to which a great deal more attention is being paid.

Efforts to monitor these contaminants so as to identify them and measure the extent of their presence involve generally the collection of samples from the air being breathed by the workers. One way to collect the particulates for study is to draw air through a filter in the breathing zone with a pump which would be packaged with its motor and power supply. Such an assembly could be clipped to the worker's belt and a hose could connect the pump to the filter holder on the brim on the safety helmet.

In a typical device of this type, as the particulate accumulates on the filter there is an increasing load on the motor and pump which results in a steady decline in the rate of air flow through the system. A consequence of this characteristic is that a measurement of total air flow over a given period of time computed from the length of operation of the pump is unreliable. For example, pumps in current use show a very marked change in air flow, e.g. .+-. 18 percent, with varying back pressure, e.g. 2 to 30 inches of water, so that additional equipment is required to obtain reliable information as the total amount of air drawn through the filter.

Other difficulties associated with previously designed equipment of this nature have to do with their cost, ability to withstand general abuse and hostile environmental conditions, and general lack of care as might be expected from the worker carrying such a device.

SUMMARY OF THE INVENTION

The present invention overcomes many of the disadvantages of present portable air sampling pumps by providing a compact, lightweight arrangement in which a disphragm is reciprocated at a constant repetition rate and stroke, and check valves are provided to permit intake and exhaust to occur, the check valves being designed especially to minimize leakage when closed. The swept volume per stroke is relatively constant. The diaphragm is provided with a large rigid section and a narrow flexible annulus so that there is no accommodation to the pressure load, that is, the back pressure. The results of the unique construction include a lightweight device which is thoroughly rugged though simple and economic to make and operate, and yet, over a back pressure which varies from 2 to 20 inches of water the flow rate remains essentially constant, e.g. .+-. 3 percent. As a result, reliable information on total air flow is obtained simply from knowledge of the total length of time the pump was operating.

It is thus a principal object of this invention to provide a portable gas pump having a uniform flow rate over a wide range of pressure loads.

Other objects and advantages of this invention will hereinafter become obvious from the following description of a preferred embodiment of this invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an elevation view in section of a preferred embodiment of the invention.

FIG. 2 shows details of a valve.

FIG. 3 shows details of a valve seat facing.

FIG. 4 shows a section along 4--4 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the figures, portable air sampling pump 10 consists of a cylindrical tube 12 in which all of the components of pump 10 are held together by a pair of retaining rings 14 and 16. Adjacent retaining ring 14 is an inlet/outlet plug 18 which is provided with an air inlet opening 22 therethrough to accommodate spud or pipe 24 and an exhaust opening 26 which may communicate by way of passageways 28 with exhaust ports 32 distributed circumferentially through the wall of cylinder 12. Opening 26, as will be noted later, is large enough to accommodate a flap element to be later described.

Pumping chamber 34 within cylindrical tube 12 is formed on one side of a diaphragm 36. A disc 38, held in place by a ring 42, shown in greater detail in FIG. 2, is made from a pliant material such as rubber and includes a pair of inlet and exhaust flap elements 44 and 46, respectively, formed by casting through disc 38 U-shaped configurations, as illustrated.

A pair of facings 48 and 52, similarly of suitable pliant material such as rubber, sandwich disc 38. As best shown in FIG. 3, facing 48 is provided with a first opening 54 which is aligned with opening 22 of plug 18 and flap element 44 of disc 38. The size of opening 54 is such as to permit flap element 44 to overlap same to a substantial degree. Facing 48 is provided with a second opening 56 which is also large enough to accommodate free movement of exhaust flap element 46 and permit relatively unimpeded air flow as shown by the arrows illustrated. A cantilever spring 57, embedded at one end in facing 48 as illustrated, or, if desired, adhered to the surface of facing 48 adjacent disc 38, extends into the opening 56 to act as a spring for flap element 46, biasing the latter against facing 52, sealing opening 62. In a similar fashion, facing 52 is provided with a large opening 58 to accommodate inlet flap element 44, a cantilever spring 59 adhered to facing 52 to bias element 44 against facing 48, and a smaller opening 62 overlapped by exhaust flap element 46.

Pump head 64 forming the opposite end of chamber 34 clamps on one side disc 38 and plug 18 the other side of pump head 64 provides one support for diaphragm 36. Head 64 is provided with suitable openings as illustrated to permit unimpeded air flow in the manner described. Facings 48 and 52 are adhered in suitable manner respectively, to plug 18 and pump head 64.

Diaphragm 36 is made from pliant material such as rubber and is provided with a flange 66 which is held in place by a retainer ring 68, pump head 64, and a solenoid head 72. It will be noted that the central region of diaphragm 36 is rendered rigid by a pair of rigid discs 74 and 76 mounted on opposite sides thereof leaving only a narrow annular region 78 which is flexible. For the purposes of this invention the radial width of the annular region 78 should be no more than about 30 percent of the radius of diaphragm 36, to maintain uniform pumping flow as buildup on the filter occurs.

Filling the remaining space within cylinder 12 is solenoid 82 having a coil 83, a slidable core 86 and a stationary core 88 with a spring 92 biasing the former to the left. Slidable core 86 is connected by way of a coupling 94 to diaphragm 36 and discs 74 and 76 through the use of a retaining ring 96 and a spring retaining ring 98. The pump stroke is not adjustable and is determined by the left end stop, when disc 74 strikes pump head 64 and the right end stop when core 86 strikes stationary core 88. A closure plug 102 having a threaded opening to accommodate a screw 104 in contact with solenoid 82 as illustrated holds the latter in place. A pair of leads 106 and 108 deliver electric power to coil 83. In the position illustrated, coil 83 is deenergized and core 86 is in the exhaust stroke by virtue of the action of spring 92, causing flapper element 46 to be open to permit exhaust whereas flapper element 44 is closed against incoming flow.

When a pulse of electrical energy is delivered by way of leads 106 and 108 to coil 83, core 82 is retracted to the right, moving the central region of diaphragm 36 to the right, causing flapper element 46 to close, and flapper element 44 to open, permitting air to enter into chamber 34. Electrical pulses are delivered from a battery source and a timing circuit, not shown, at a uniform rate independent of the load on pump 10 so that the repetition rate is not affected thereby. Any suitable portable power source and a timing circuit as known in the art for delivering electrical pulses at a uniform rate would be satisfactory for purposes of this invention, or if desired, a stationary source may be employed, with a lead line extending to the person carrying pump 10. Because of the lightweight and efficient design of pump 10, only a relatively small amount of electrical power is required. An example of a power source which has been employed successfully is a nickel cadmium battery, Gould alkaline No. 400703, 12 V 225 ma hours, and a timing circuit as described in IEEE second International Geoscience Symposium Digest of Technical Papers, Washington, D.C., Apr. 14-17, 1970, pp 17-1 through 17-4, "Impulse Drive Recorder" by S. Frederic Guggenheim and Norman Latner.

In the operation of the apparatus described, diaphragm 36 is reciprocated at a uniform rate by solenoid 82, air entering chamber 34 through inlet pipe 24 and opening 54 in facing 48 during suction with diaphragm 36 retracted to the right and exhaust flapper element 46 closed by the combination of suction and the action of cantilever spring 57, and air then exhausted through opening 62 during the reverse stroke of diaphragm 36 as illustrated.

Cantilever springs 57 and 59 insure that there is rapid and complete closure of flapper elements 46 and 44, while the substantial overlapping of the latter elements of the facing surfaces surrounding openings 62 and 54 and their construction of pliant material insure that there is a minimum of leakage. These features all contribute to the effectiveness of the pump.

It is thus seen that there has been provided a lightweight, portable pump of economic and practical construction. The diaphragm acts like a piston with all of its advantages but at the same time it is light in weight and mass, requires fewer moving parts and has no leakage past its sides. The whole assembly of the pump requires only four snap rings and one screw assembled inside of a cylinder so that it is simple and inexpensive to make and to maintain and is resistant to rough usage in the field under adverse conditions. The valves provide for rubber to rubber contact and due to their light weight and mass they open and close rapidly with virtually no leakage after closing.

Another feature of this invention is the use of positive stops at the end of each stroke of diaphragm 36. Therefore, the volume swept at each stroke is constant. The pump air volume delivery may be varied only by shortening or lengthening the time between strokes (changing the pulse frequency of the electronic circuit). The electrically powered stroke to the right is at high speed (about 30 to 50 milliseconds). This stroke instantaneously creates a partial vacuum between the pump and the filter that is upstream of inlet pipe 24, and in the elapsed time to the next intake stroke, air flows through the filter to relieve or reduce the vacuum and restore essentially atmospheric pressure between the filter and a minimum elapsed time between pump power strokes. It is an essential concomitant to the maintenance of constant volume air flow with increasing pressure drop across the filter.

Claims

What is claimed:

1. A compact, lightweight gas pump for delivering said gas at a substantially constant flow rate over a wide range of back pressure comprising:

a. first and second wall means forming therebetween a chamber;

b. said first wall means having a rigid central section and a flexible annular section;

c. said second wall means having formed therein a pair of inlet and outlet flap elements;

d. first and second valve walls adjacent opposite sides of said second wall means, said first valve wall being within said chamber and having an exhaust opening controlled by the outlet flap element and an opening to permit inlet flow, and said second valve wall having an inlet opening controlled by the inlet flap element and an opening to permit exhaust flow;

e. means in said first and second walls for biasing said flap elements into closing their respective inlet and exhaust openings; and

f. means for reciprocating said rigid central section of said first wall means to cause exhaust of said gas as said first wall means moves toward said second wall means and intake of said gas as said first wall means moves away from said second wall means.

2. The pump of claim 1 in which mechanical stops are provided to limit the stroke of said first wall means in each direction.

3. The pump of claim 2 in which the radial width of said flexible annular section is no more than 30 percent of the radius of said first wall means.

4. The pump of claim 3 in which second wall means and said first and second valve walls are made from pliant material.