GB1570390A

GB1570390A - Device for measuring liquid flow

Info

Publication number: GB1570390A
Application number: GB5126175A
Authority: GB
Original assignee: National Research Development Corp UK; National Research Development Corp of India
Current assignee: National Research Development Corp UK; National Research Development Corp of India
Priority date: 1976-12-09
Filing date: 1976-12-09
Publication date: 1980-07-02

Description

(54) DEVICE FOR MEASURING LIQUID FLOW (71) We, NATIONAL RESEARCH DE VELOPMENT CORPORATION, a British Corporation established by Statute, of Kingsgate House, 66-74 Victoria Street, London, S.W.1. do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a device for measuring the flow of a liquid, particularly at very low flow rates.

In biological, microbiological, and bateriological apparatus, it may be necessary to measure flow rates of the order of millilitres per hour without interrupting the supply of liquid to the apparatus. Usually it is a further requirement that the risks of microbial contamination and of supplying a gas such as air instead of the liquid are substantially eliminated.

According to the invention, apparatus for measuring the flow of a liquid through a flow tube comprises closure means for selectively closing the flow tube; and a closure bypass means comprising a volume-calibrated tube disposed above the level of the flow tube and connected at its lower end to the flow tube upstream of the closure means, a reservoir container connected to the flow tube downstream of the closure means and having above the level of the flow tube a portion of its volume greater than the total volume of the volume-calibrated tube, and a fluid-tight connection between the upper end of the volume-calibrated tube and the upper end of the reservoir container.

For automatic operation the apparatus further comprises two liquid-sensing means adjacent the volumecalibrated tube and dis Dosed at different heights, and means for indicating the lapse of time between the sensing of liquid by the lower and by the upper sensing means.

Also according to the invention, a method of measuring the rate of flow of a liquid through a flow tube comprises closing the tube at a known position along its length; diverting the liquid upstream of the closed part of the tube into a volume-calibrated tube so as to displace a volume of gas from the volume-calibrated tube into a reservoir of the liquid, and to displace a volume of liquid from the reservoir into the flow tube downstream of the closed part, whereby the supply of liquid from the flow tube is not interrupted; measuring the time taken for a known volume of liquid to flow into the volume-calibrated tube; and reopening the flow tube.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 illustrates an apparatus for measuring the flow rate of a liquid; and Figure 2 illustrates an electrical control circuit for automatic operation of the apparatus shown in Figure 1.

In Figure 1, a liquid is pumped by a peristaltic pump 8 from a liquid supply, as indicated by the arrow A, and passes through a tube 12 to a chemostatic apparatus (not shown) as indicated by the arrow B. The tube 12 can be closed by a clamp 14. Upstream of the clamp, the tube 12 is connected to a T-shaped connector 16 arranged in an inverted position so that liquid can flow from the pump 8 to the tube 12 through the arms forming the cross of the T and with the third arm of the connector connected to a graduated glass tube 18 which is vertical and above the T-piece.

Downstream of the clamp 14 is a reservoir 20 which comprises a hollow vessel having two lower connecting tubes 22, 24 through which liquid can flow from tube 12 to the chemostat, and an upper, vertical, connecting tube 26 which is connected by a flexible tube 28 to the upper end of the graduated tube 18. The volume of reservoir 20 is considerably greater than the combined volume of the graduated tube 18 and the flexible tube 28.

Initially, the apparatus contains no liquid and clamp 14 is open. The reservoir is inverted about tube 26 and liquid is pumped through the tube 22, displacing air from the reservoir through connecting tube 24. When the reservoir is almost full, it is turned to its normal operating position. Air s now trapped in tubes 18 and 28 and the meniscus in tube 18 is arranged to be just below the graduations.

If the clamp 14 is now closed, the pump causes the liquid to rise in the tube 18; the time taken for the meniscus to rise between chosen graduations can be measured using a stop watch, and the flow rate can be calculated. As the liquid rises in tube 18, the liquid level falls in the reservoir 20 so that the liquid supply to the chemostat need not be interrupted. The volume of the reservoir is chosen so that it still contains a considerable quantity of liquid when the liquid level in tube 18 reaches the top of the tube, and there is minimum risk of any air being supplied to the chemostat. If the level is allowed to rise in tube 18 so as to fill that tube and then run down through tube 18 into the reservoir then liquid is still supplied to the chemostat not air. The risk of contamination is also minimised.

Typically the graduated tube 18 may be a 0.1 to 1.0 millilitre serological pipette coated internally with a water repellant material, or a polypropylene pipette, and liquid flow rates of less than 10 millilitres per hour can be measured.

Preferably the apparatus is arranged at the lowest point in the system so that slight positive hydrostatic pressure is present throughout the medium supply tube from the supply reservoir (not shown) and throughout the medium supply tube to the chemostat. This prevents the development of air bubbles otherwise caused by gaseous diffusion in through the walls of the supply and delivery tubes and tube 12 which are typically of silicone rubber. Diffusion of air out through the walls of flexible tube 28 can be minimised by the use of tubing with low air permeability characteristic.

While the rise of the liquid in tube 18 can be measured using a stop watch, automatic measurement is also possible. The sensor heads 30, 32 of two liquid sensing modules 31, 33 are placed adjacent the tube 18 at vertically spaced positions. Each head can detect the presence of liquid in the tube 18. The heads are connected to the electrical circuit shown in Figure 2; for automatic measurement the clamp 14 comprises a normally-closed solenoid valve 14A.

As shown in Figure 2, the modules 31, 33 having relay contacts d, e and f, g respectively, are connected to a digital time indicator 34 and to an auxiliary relay 36 which has contacts a, b, c. The circuit components are supplied from a mains supply, and the circuit contains several switches S1 to S6. The relay contacts d, e, f and g are shown in the position in which the respective liquid sensor heads indicate that liquid is present in the tube 18, i.e. the meniscus is above the head 32 (Figure 1).

Initially, liquid is at the position shown in Figure 1 with the meniscus below tube 18.

In operation, the mains switch S1 is closed, push button switch S2 is closed momentarily so that power is supplied to the auxiliary relay 36, and contacts a and b close and c opens. Contact a provides one connection to the timing circuit of the time indicator 34; contact b supplies power to relay 36, thereby keeping contacts a and b closed and c open even when the switch S2 is allowed to open; and the opening of contact c closes the solenoid valve 14A so that liquid starts to rise in the graduated tube. When the liquid reaches sensor head 30, contact d closes and e opens to the positions shown; d supplies the second connection to the time indicator 34 which starts to measure time; and the opening of contact e isolates switch S2.When the liquid in tube 18 reaches sensor head 32, contacts f and g open to the position shown in the Figure; opening contact f stops the time indicator which provides a display of the measured time interval; opening contact g de-energises the auxiliary relay 36 so that contacts a and b open and c closes. Closing contact c opens the solenoid valve 14A and the liquid level in tube 18 falls; opening contact a provides a second break in the time indicator circuit. As the liquid level falls, the relays in modules 31 and 33 switch back to their starting positions.

The display of the measured time interval is maintained until sensor head 30 senses liquid during the next cycle of operation, which causes the time indicator to be reset.

If required, the display could be in the form of a flow rate.

As an alternative mode of operation.

switch 53 is closed instead of switch 52.

This provides repeated cycling -- when the liquid falls o the level of sensor head 30.

the solenoid valve is operated immediately, the liquid rises in tube 18 again, and the time indicator 34 starts timing the next cycle.

During calibration of the device the graduations on tube 18 at which the sensor heads 30 and 32 operate must be known so that the volume of liquid timed by the apparatus can be calculated. A second auxiliary relay 38 and switch S4 allow the rise of the liquid in tube 18 to be stopped when sensor head 30 operates. When switch S4 is closed and the liquid rises to operate sensing module 31. opening of contact e causes relay 38 to operate and disconnect power from the pump 8, and simultaneously causes a buzzer 40 to sound. The position of the meniscus can be read off. Switch 55 is then operated to reset the apparatus by de-energising relay 36 and opening the solenoid valve 14A.Switch S6 provides a similar pump-stop signal when module 33 operates, with the additional feature that the solenoid valve 14A is held closed.

The circuit also contains indicator lamps at suitable positions.

The liquid flow will have superimposed pulsations due to the operation of the pump.

It will usually be necessary to make several measurements of time for a single flow ate, and to take a mean.

WHAT WE CLAIM IS: 1. Apparatus for measuring the flow of a liquid through a flow tube comprises closure means for selectively closing the flow tube; and closure bypass means comprising a volume-calibrated tube disposed above the level of the flow tube and con necked at its lower end to the flow tube upstream of the closure means, a reservoir container connected to the flow tube downstream of the closure means and having above the level of the flow tube a portion of its volume greater than the total volume of the volume-calibrated tube, and a fluidtight connection between the upper end of the volume-calibrated tube and the upper end of the reservoir container.

2. Apparatus according to Claim 1 further comprising two liquid-sensing means adjacent the volume-calibrated tube and disposed at different heights; and means for indicating the lapse of time between the sensing of liquid by the lower and by the upper sensing means.

3. A method of measuring the rate of flow of a liquid through a flow tube comprising closing the tube at a known position along its length; diverting the liquid upstream of the closed part of the tube into a volume-calibrated tube so as to displace a volume of gas from the volumecalibrated tube into a reservoir of the iiquid, so as to displace a volume of liquid from the reservoir into the flow tube downstream of the closed part, whereby the supply of liquid from the flow tube is not interrupted; measuring the time taken for a known volume of liquid to flow into the volume calibrated tube; and reopening the flow tube.

4. Apparatus for measuring the flow of a liquid through a flow tube substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

30 operates. When switch S4 is closed and the liquid rises to operate sensing module 31. opening of contact e causes relay 38 to operate and disconnect power from the pump 8, and simultaneously causes a buzzer 40 to sound. The position of the meniscus can be read off. Switch 55 is then operated to reset the apparatus by de-energising relay 36 and opening the solenoid valve 14A. Switch S6 provides a similar pump-stop signal when module 33 operates, with the additional feature that the solenoid valve 14A is held closed.

The circuit also contains indicator lamps at suitable positions.

The liquid flow will have superimposed pulsations due to the operation of the pump.

It will usually be necessary to make several measurements of time for a single flow ate, and to take a mean.

WHAT WE CLAIM IS: 1. Apparatus for measuring the flow of a liquid through a flow tube comprises closure means for selectively closing the flow tube; and closure bypass means comprising a volume-calibrated tube disposed above the level of the flow tube and con necked at its lower end to the flow tube upstream of the closure means, a reservoir container connected to the flow tube downstream of the closure means and having above the level of the flow tube a portion of its volume greater than the total volume of the volume-calibrated tube, and a fluidtight connection between the upper end of the volume-calibrated tube and the upper end of the reservoir container.
2. Apparatus according to Claim 1 further comprising two liquid-sensing means adjacent the volume-calibrated tube and disposed at different heights; and means for indicating the lapse of time between the sensing of liquid by the lower and by the upper sensing means.
3. A method of measuring the rate of flow of a liquid through a flow tube comprising closing the tube at a known position along its length; diverting the liquid upstream of the closed part of the tube into a volume-calibrated tube so as to displace a volume of gas from the volumecalibrated tube into a reservoir of the iiquid, so as to displace a volume of liquid from the reservoir into the flow tube downstream of the closed part, whereby the supply of liquid from the flow tube is not interrupted; measuring the time taken for a known volume of liquid to flow into the volume calibrated tube; and reopening the flow tube.
4. Apparatus for measuring the flow of a liquid through a flow tube substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.