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Transcript
Flow Meters Flow: Volume of a fluid passing certain point 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. • Consists of :Flow tube_Float(bobbin) _Control knob . • Flow is affected by the viscosity&density • At low flow : viscosity • At high flow: density. • 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. • Flow tube :Conical glass tube. • Low flow tube graduated/100 ml/min. up to one liter • High flow tube graduated/1L/min.up to 10L/min. • 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 . 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 . • Non spinning bobbin that may indicate O2 is flowing while the bobbin is stucked with no adequate flow hypoxic mixture. • The density of a gas is dependent on the • • • ambient pr . 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 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 . Static charges can be dealt with by bimetallic strip . Dirts & dusts by air filter proximal to the needle valve. 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 . • If axial push _ pull forces are applied to the needle valve spindle the flow change must not exceed 10% . O2/N2O Ratio Controllers • In modern anesth. ,there is interconnect. Of N2O & O2 flowmeters to ensure delivery of a conc.of at least 25% O2 . • 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 O2 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. • O2 flow can not be completely turned off. A minimum flow rate of 200_450 ml/min is delivered to provide sufficient O2 for the basal metabolic needs by : 1. Applicat. Of resistor in the oxygen pipeline. 2. OR/stop screw on O2 control valve. • The control knob of O2 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 2. 3. 4. 5. 6. 7. Coxter flow meter Bubble flow meter Rotor meter Wright’s spirometer Pneumotachographs (Vitalograph) Ultrasonic flowmeters Electronic magnetic flowmeter