Flow MetersFlow Meters

Flow: Volume of a fluid passing certain Flow: Volume of a fluid passing certain point point

over a given time Flow Rate.over a given time Flow Rate.

Flow meters:sets used to measure flow Flow meters:sets used to measure flow either gas or liquid either gas or liquid

Gas Flow MeasurementsGas Flow Measurements

• Rotameter:variable orifice constant Rotameter:variable orifice constant pr.device to control the flow of fresh pr.device to control the flow of fresh gas from the anesth.machine to the gas from the anesth.machine to the pt.breath.circ.pt.breath.circ.

• Consists of :Flow tube_Float(bobbin) Consists of :Flow tube_Float(bobbin) _Control knob . _Control knob .

• Flow is affected by the Flow is affected by the viscosity&densityviscosity&density

• At low flow : viscosityAt low flow : viscosity• At high flow: density.At high flow: density.• So,each type of gas requires diff. So,each type of gas requires diff.

calibrated flow tube.calibrated flow tube.• The flow tubes designed for one gas The flow tubes designed for one gas

should not be interchanged with should not be interchanged with another hypoxic mixtures. another hypoxic mixtures.

• Flow tube :Conical glass tube.Flow tube :Conical glass tube.

• Low flow tube Low flow tube graduated/100 ml/min. up to one litergraduated/100 ml/min. up to one liter

• High flow tube High flow tube graduated/1L/min.up to 10L/min.graduated/1L/min.up to 10L/min.

• Control knob :when it is turned Control knob :when it is turned needle valve is opened.needle valve is opened.

• Gas flows into the bottom of the flow Gas flows into the bottom of the flow tube & moves upward around the tube & moves upward around the bobbin upward force pushes the bobbin upward force pushes the bobbin up in the tube . bobbin up in the tube .

Float (bobbin)Float (bobbin)

• It may be balls or cylindrical with It may be balls or cylindrical with slots in its upper part & tapered base slots in its upper part & tapered base to make it to rotate in the gas stream to make it to rotate in the gas stream . .

• Non spinning bobbin that may Non spinning bobbin that may indicate Oindicate O2 2 is flowing while the is flowing while the bobbin is stucked with no adequate bobbin is stucked with no adequate flow hypoxic mixture.flow hypoxic mixture.

• The density of a gas is dependent on the The density of a gas is dependent on the ambient pr .ambient pr .

• Large diff. in atmosph. Pr. alter the Large diff. in atmosph. Pr. alter the calibrat.of flow tube .calibrat.of flow tube .

• At high altitudes with hypobaric condit. At high altitudes with hypobaric condit. Flow meter setting is less than the actual Flow meter setting is less than the actual

• At hyperbaric condition flow setting is At hyperbaric condition flow setting is more than the actual hypoxic more than the actual hypoxic mixturemixture

• The spinning movement of the bobbin can The spinning movement of the bobbin can be affected by dust , dirt & static electric be affected by dust , dirt & static electric charges .charges .

• Static charges can be dealt with by Static charges can be dealt with by bimetallic strip .bimetallic strip .

• Dirts & dusts by air filter proximal to the Dirts & dusts by air filter proximal to the needle valve.needle valve.

• Slots on the bobbin to spin resist the effect Slots on the bobbin to spin resist the effect of static charges & dust.of static charges & dust.

• The twist required to turn the knobs The twist required to turn the knobs must be sufficient to prevent must be sufficient to prevent accidental readjustment from casual accidental readjustment from casual knock .knock .

• If axial push _ pull forces are applied If axial push _ pull forces are applied to the needle valve spindle the flow to the needle valve spindle the flow change must not exceed 10% .change must not exceed 10% .

OO22/N/N22O Ratio ControllersO Ratio Controllers

• In modern anesth. ,there is In modern anesth. ,there is interconnect. Of Ninterconnect. Of N22O & OO & O2 2 flowmeters flowmeters to ensure delivery of a conc.of at least to ensure delivery of a conc.of at least 25% O25% O22 . .

• There are 2 systems :-There are 2 systems :-

1.1. Pneumatic syst. ORMC (designed Pneumatic syst. ORMC (designed by Drager). by Drager).

2.2. Chain _link 25 proportion (by Ohmeda )Chain _link 25 proportion (by Ohmeda )

Safety Measures (additional)Safety Measures (additional)

1.1. The flow tube for oxygen has been The flow tube for oxygen has been on the extreme rt. Side Oon the extreme rt. Side O22 is is the last gas to be added to the the last gas to be added to the fresh gas supply.fresh gas supply.

2.2. A color _coded flow control knob is A color _coded flow control knob is located under its respective flow located under its respective flow tube.tube.

3.3. A color_coded cylinder pr. gauge for A color_coded cylinder pr. gauge for the gas entering the flowmeter & the gas entering the flowmeter & located under its respective located under its respective flowmeter.flowmeter.

4.4. A plastic screen used to prevent A plastic screen used to prevent damage to the flowmeters.damage to the flowmeters.

5.5. In some machines , protective bar In some machines , protective bar placed infront of the flow meters to placed infront of the flow meters to protect from accidental bumping. protect from accidental bumping.

6.6. Lighting system for the flow meter Lighting system for the flow meter is valuable when the op.room light is valuable when the op.room light is dimmed .is dimmed .

7.7. Flow tube pin _indexing syst. to Flow tube pin _indexing syst. to prevent interchange of flow meter prevent interchange of flow meter units hypoxic mixture. units hypoxic mixture.

• OO22 flow can not be completely turned flow can not be completely turned off. A minimum flow rate of 200_450 off. A minimum flow rate of 200_450 ml/min is delivered to provide ml/min is delivered to provide sufficient Osufficient O22 for the basal metabolic for the basal metabolic needs by :needs by :

1.1. Applicat. Of resistor in the oxygen Applicat. Of resistor in the oxygen pipeline.pipeline.

2.2. OR/stop screw on OOR/stop screw on O2 2 control valve.control valve.

• The control knob of OThe control knob of O2 2 has esp. has esp. shape:shape:

OctagonalOctagonal Greater diameterGreater diameter Project beyond the other knobsProject beyond the other knobs

Other types of flow metersOther types of flow meters

1.1. Electronic flow meterElectronic flow meter

a.a. Oscillations of pr. Drop across an Oscillations of pr. Drop across an orifice is proportional to the flow rateorifice is proportional to the flow rate

b.b. Thermister flow meter : Thermister flow meter : Gas flow affects thermocouple Gas flow affects thermocouple

attached to either end of flow tube attached to either end of flow tube

2.2. Coxter flow meterCoxter flow meter

3.3. Bubble flow meterBubble flow meter

4.4. Rotor meter Wright’s Rotor meter Wright’s spirometerspirometer

5.5. Pneumotachographs (Vitalograph)Pneumotachographs (Vitalograph)

6.6. Ultrasonic flowmetersUltrasonic flowmeters

7.7. Electronic magnetic flowmeterElectronic magnetic flowmeter