AU637737B1

AU637737B1 - Fume cupboard with variable air flow

Info

Publication number: AU637737B1
Application number: AU90003/91A
Authority: AU
Inventors: Ronald Edmond Lucas
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-07-10
Filing date: 1991-12-23
Publication date: 1993-06-03
Anticipated expiration: 2007-07-10

Description

6377 37 S F Ref: 200282 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

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FOR OFFICE USE: Class Int Class

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Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name and Address of Applicant: Inventor(s): Address for Service: Ronald Edmond Lucas 228 Barrenjoey Road Newport New South Wales 2106

AUSTRALIA

Ronald Edmond Lucas Spruson Ferguson, Patent Attorneys, Level 33 St Martins Tower, 31 Market Street, Sydney, New South Wales, 2000, Australia S. S a S

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S. S I' S 5 @5 Complete Specification for the invention entitled: Fume Cupboard with Variable Air Flow The following statement is a full description of this invention, including the best method of performing it known to me/us 5846/3 This invention relates to fume cupboards.

Apparatus of this kind is intended to provide a partial enclosed work place for minimising the spread of fumes to operators, and other personnel. Ventilation is provided by an induced flow of air through a working aperture which dilutes the fumes by means of an extraction system containing a fan and provides for the release of the fumes remotely and safely. A vertically movable transparent sash covering the working aperture provides access to a working area. Fume cupboards are mainly fitted in laboratories.

Strict requirements are determined by the Standards Associations of various countries with respect to the minimum safe capture velocity across the sash when fully opened. The above requirements create two major problems which are well known and attempts at solution have not been entirely successful. One problem has been the creation of 0000, 15 objectionably high air velocity at low sash openings, which has deleterious effects upon the work being performed within the cupboard.

*It is conventional practice to provide a by-pass to allow air to flow into the fume cupboard chamber other than through the working aperture, with the objective of preventing excessively high face velocities at low sash openings.

However, there are numerous disadvantages in the use of a by-pass, J such as the possibility of fumes escaping therethrough, and the unnecessary evacuation from the laboratory of conditioned air, which would be avoided if means were employed merely to reduce the total 25 evacuating air flow as the sash is lowered.

S" It is the main object of this invention to provide a simple and effective means of controlling the flow of air through the working aperture of a fume cupboard without the use of a by-pass.

To this end, the invention provides a fume cupboard comprising a housing, a displaceable sash at one part of the housing, a working chamber within said housing accessible to a user via said sash, exhaust ducting for the chamber, an electrical extraction fan connected with the ducting, and control means connected to respond to displacement of said sash to effect an adjustment of the speed of said fan to control the air flow through the working chamber wherein said control comprises a speed controller connected to the fan motor activated by proximity or micro switches fitted to the sash mechanism.

STA/0233E 3 The invention will be described in more detail with reference to t;ie accompanying drawings, in which: Fig. 1 diagrammatically represents a fume cupboard to which the present invention has been applied.

The arrangement of the invention is incorporated, as shown in Fig. 1, within the housing 21 of the fume cupboard 20 which is gererally of conventional form, excepting that no by-pass is included. A sash 3 is located upon the front face 22 of the cupboard 20 to slide vertically within a working aperture 23 thereof between minimum and maximum sash openings. An internal chamber 24 accessed thereby within the cupboard is evacuated in known fashion by ducting 25 connected to the housing 21 and at the exhaust end 26 of wh'ch is provided an electrical extraction 0' fan 27. Electrical power is provided to a driving motor 28 for the fan 0.0 27 by suitable power line 29.

15 With reference to Fig. 1 the sash 3 is connected by a sash card via o overhead pulleys to a counter balance weight or weights. Thus the sash

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.00. can be raised by the operator for insertion of work material within the chamber 24 of the fume cupboard, or lowered to enable processing of the material to commence safely.

According to this invention proximity switches 32 of any number from 1 upward are located adjacent to the sash channel. The sash frame contains one or more magnets 33 fixed to the moving side which when passing the fixed position of the proximity switch will send a signal via a multiple pre set module 13 to the speed controller 30 connected to the 2 25 fan motor 28 thereby altering the speed of the fan 27. A multiple pre-set speed module is triggered by input logic from one or more contacts or switches of practically any kind and changes the fan speed from one pre-selected speed to another, quickly, in response to the input logic. A master chassis type variable motor speed controller 30 which may be mounted on the top and exterior of the fume cupboard housing 21, receives the output from the multiple pre set electronic module. One suitable form of speed controller 30 is that marketed by Control Techniques Australia Pty Ltd as VC55 to 150. Other suitable controllers may be obtained from Reynold Australia Pty. Ltd. (Model VF 175) AND Varidrive Pty. Ltd. (Zener Model). The output of the speed controller is connected by line 29 to the fan motor 28 which is preferably 3 phase, /4 HP operative at 1,440 RPM and energised via the speed controller from a single phase supply. The fan 27 is preferably a centrifugal STA/0233E -4type fan. The arrangement is such that with raising of the sash 3 and therefore activating one or more of the proximity switches 32 the speed of the fan 27 will be increased to a predetermined level previously pre selected on the Multiple Pre Set Electronic Module 13.

It is preferable to provide an emergency override button switch 31 connected to the front face 22 of cupboard 20 which may by-pass the signal from the Multiple Pre Set Module and provide maximum speed from the fan motor. With release of the button switch 31 by the operator the power supply would be returned to its automatically controlled condition.

In the alternative to the activating proximity switches 32 micro switches and suitable cams may be used to send a signal to the speed controller via the Multiple Pre Set Module.

Nhereas a preferred embodiment has been described in the foregoing passages it should be understood that other forms, modifications and 1 5 refinements are feasible within the scope of this invention.

In some instances, to avoid excessively low outlet velocity from 00:0 the exhaust ducting at minimum sash opening, a motorised rotatable damper, also driven from the controller 30, may be incorporated in the ducting near the exhaust outlet and arranged to close to increase the air velocity according to sash position.

It is not essential that the proximity switches be fitted to the s: sash frame, they may be positioned elsewhere on the fume cupboard to be 00 6 activated by magnets fitted to the sash counter balance weight. The same result is achieved.

loom•: 00 0 0 0 0 STA/0233E

Claims

1. A fume cupboard comprising a housing, a displaceable sash at one part of the housing, a working chamber within said housing accessible to a user via said sash, exhaust ducting for the chamber, an electrical extraction fan connected with the ducting, and control means connected to respond to displacement of said sash to effect an adjustment of the speed of said fan to control the air flow through the working chamber, wherein said control means comprises a speed controller connected to the fan motor and proximity or micro switches providing a signal to the speed controller.

2. A fume cupboard according to claim 1, wherein said fan is a centrifugal type fan.

3. A fume cupboard according to either claim 1 or claim 2, 'further comprising an emergency override switch operative to by-pass any other signal to the speed controller to provide maximum speed from the fan.

4. A fume cupboard according to any one of the preceding claims, further comprising a motorised rotatable damper positioned within said exhaust ducting adjacent the outlet thereof and also controlled from said control means to increase the velocity of exhausting air at low sash openings of said cupboard. I

5. A fume cupboard according to any one of the preceding claims, wherein switches are located adjacent to the sash weight position and activated by magnets or cams fitted to the sash weight or cord.

6. A fume cupboard according to any one of the preceding claims wherein the fan speed is varied by a multiple pre-set speed module in response to a logic signal provided by said switches.

7. A fume cupboard substantially as hereinbefore described with *reference to Figure 1. DATED this EIGHTEENTH day of DECEMBER 1991 Ronald Edmond Lucas Patent Attorneys for the Applicant SPRUSON FERGUSON STA/0233E ABSTRACT FUME CUPBOARD WITH VARIABLE AIR FLOW The invention comprises a fume cupboard. The cupboard (20) has a housing. There is a displaceable sash at one part of the housing, a working chamber (24) within said housing, exhaust ducting (25) for the chamber, and an electrical extraction fan (27) connected with the ducting. Control means respond to displacement of the sash to effect an adjustment of the speed of said fan to control the air flow through the working chamber. The control means comprises a speed controller connected to the fan motor activated by proximity (32) or micro switches fitted to the sash mechanism. 4j Fig.1 9 d *bl a ea 6Ouh 4ar 6* 9 9 4 *6 a. a(I 4 STA/0233E