Flow Meters Flow: Volume of a fluid passing certain point over a given time Flow Rate. over a given time Flow Rate. Flow meters:sets used to measure flow either gas or liquid

Gas Flow Measurements Rotameter:variable orifice constant pr.device to control the flow of fresh gas from the anesth.machine to the pt.breath.circ. Rotameter:variable orifice constant pr.device to control the flow of fresh gas from the anesth.machine to the pt.breath.circ. Consists of :Flow tube_Float(bobbin) _Control knob. Consists of :Flow tube_Float(bobbin) _Control knob.

Flow is affected by the viscosity&density Flow is affected by the viscosity&density At low flow : viscosity At low flow : viscosity At high flow: density. At high flow: density. So,each type of gas requires diff. calibrated flow tube. So,each type of gas requires diff. calibrated flow tube. The flow tubes designed for one gas should not be interchanged with another hypoxic mixtures. The flow tubes designed for one gas should not be interchanged with another hypoxic mixtures.

Flow tube :Conical glass tube. Flow tube :Conical glass tube. Low flow tube graduated/100 ml/min. up to one liter Low flow tube graduated/100 ml/min. up to one liter High flow tube graduated/1L/min.up to 10L/min. High flow tube graduated/1L/min.up to 10L/min.

Control knob :when it is turned needle valve is opened. Control knob :when it is turned needle valve is opened. Gas flows into the bottom of the flow tube & moves upward around the bobbin upward force pushes the bobbin up in the tube. Gas flows into the bottom of the flow tube & moves upward around the bobbin upward force pushes the bobbin up in the tube.

Float (bobbin) It may be balls or cylindrical with slots in its upper part & tapered base to make it to rotate in the gas stream. It may be balls or cylindrical with slots in its upper part & tapered base to make it to rotate in the gas stream. Non spinning bobbin that may indicate O 2 is flowing while the bobbin is stucked with no adequate flow hypoxic mixture. Non spinning bobbin that may indicate O 2 is flowing while the bobbin is stucked with no adequate flow hypoxic mixture.

The density of a gas is dependent on the ambient pr. The density of a gas is dependent on the ambient pr. Large diff. in atmosph. Pr. alter the calibrat.of flow tube. Large diff. in atmosph. Pr. alter the calibrat.of flow tube. At high altitudes with hypobaric condit. Flow meter setting is less than the actual At high altitudes with hypobaric condit. Flow meter setting is less than the actual At hyperbaric condition flow setting is more than the actual hypoxic mixture At hyperbaric condition flow setting is more than the actual hypoxic mixture

The spinning movement of the bobbin can be affected by dust, dirt & static electric charges. The spinning movement of the bobbin can be affected by dust, dirt & static electric charges. Static charges can be dealt with by bimetallic strip. Static charges can be dealt with by bimetallic strip. Dirts & dusts by air filter proximal to the needle valve. Dirts & dusts by air filter proximal to the needle valve. Slots on the bobbin to spin resist the effect of static charges & dust. Slots on the bobbin to spin resist the effect of static charges & dust.

The twist required to turn the knobs must be sufficient to prevent accidental readjustment from casual knock. The twist required to turn the knobs must be sufficient to prevent accidental readjustment from casual knock. If axial push _ pull forces are applied to the needle valve spindle the flow change must not exceed 10%. If axial push _ pull forces are applied to the needle valve spindle the flow change must not exceed 10%.

O 2 /N 2 O Ratio Controllers In modern anesth.,there is interconnect. Of N 2 O & O 2 flowmeters to ensure delivery of a conc.of at least 25% O 2. In modern anesth.,there is interconnect. Of N 2 O & O 2 flowmeters to ensure delivery of a conc.of at least 25% O 2. There are 2 systems :- There are 2 systems :- 1. Pneumatic syst. ORMC (designed by Drager). 2. Chain _link 25 proportion (by Ohmeda )

Safety Measures (additional) 1. The flow tube for oxygen has been on the extreme rt. Side O 2 is the last gas to be added to the fresh gas supply. 2. A color _coded flow control knob is located under its respective flow tube.

3. A color_coded cylinder pr. gauge for the gas entering the flowmeter & located under its respective flowmeter. 4. A plastic screen used to prevent damage to the flowmeters. 5. In some machines, protective bar placed infront of the flow meters to protect from accidental bumping.

6. Lighting system for the flow meter is valuable when the op.room light is dimmed. 7. Flow tube pin _indexing syst. to prevent interchange of flow meter units hypoxic mixture.

O 2 flow can not be completely turned off. A minimum flow rate of 200_450 ml/min is delivered to provide sufficient O 2 for the basal metabolic needs by : O 2 flow can not be completely turned off. A minimum flow rate of 200_450 ml/min is delivered to provide sufficient O 2 for the basal metabolic needs by : 1. Applicat. Of resistor in the oxygen pipeline. 2. OR/stop screw on O 2 control valve.

The control knob of O 2 has esp. shape: The control knob of O 2 has esp. shape:  Octagonal  Greater diameter  Project beyond the other knobs

Other types of flow meters 1. Electronic flow meter a. Oscillations of pr. Drop across an orifice is proportional to the flow rate b. Thermister flow meter : Gas flow affects thermocouple attached to either end of flow tube Gas flow affects thermocouple attached to either end of flow tube

2. Coxter flow meter 3. Bubble flow meter 4. Rotor meter Wright’s spirometer 5. Pneumotachographs (Vitalograph) 6. Ultrasonic flowmeters 7. Electronic magnetic flowmeter