HEADING 90.26 - INSTRUMENTS AND APPARATUS FOR MEASURING OR CHECKING THE FLOW LEVEL PRESSURE OR OTHER VARIABLES OF LIQUIDS OR GASES (FOR EXAMPLE FLOWMETERS LEVEL GAUGES MANO METERS HEAT METERS) EXCLUDING INSTRUMENTS AND APPARATUS OF HEADING No. 90.14 90.15 90.28 OR 90.32. 51 COMMODITIES
9026.10 - For measuring or checking the flow or level of liquids
9026.20 - For measuring or checking pressure
9026.80 - Other instruments or apparatus
9026.90 - Parts and accessories
Apart from instruments or apparatus more specifically covered by other headings of the Nomenclature such as :
(a)Pressure-reducing valves and thermostatically controlled valves (heading 84.81); (b)Anemometers (wind gauges) and hydrological level gauges (heading 90.15);
(c)Thermometers pyrometers barometers hygrometers and psychrometers (heading 90.25); (d)Instruments and apparatus for physical or chemical analysis etc. (heading 90.27) this heading covers instruments and apparatus for measuring or checking the flow level pressure kinetic energy or other process variables of liquids or gases. The instruments and apparatus of this heading may be fitted with recording signalling or optical scale-reading devices or transmitters with an electrical pneumatic or hydraulic output.
Measuring checking apparatus generally incorporates an element sensitive to variations in the quantity to be measured (e.g. Bourdon tube diaphragm bellows semiconductors) moving a needle or a pointer. In some devices the variations are converted into electrical signals. Measuring or checking instruments or apparatus of this heading combined with taps valves etc. are to be classified as indicated in the Explanatory Note to heading 84.81.
(I) APPARATUS FOR MEASURING OR CHECKING THE FLOW OR RATE OF FLOW OF LIQUIDS OR GASES
(A) Flowmeters. These indicate the rate of flow (in volume or weight per unit of time) and are used for measurement of flow both through open channels (rivers waterways etc.) and through closed conduits (piping etc.). Some flowmeters use the principle of the fluid meters of heading 90.28 (turbine- type piston-type etc.) but the majority are based on the principle of differential pressure. These include :
(1) Differential pressure (fixed aperture) flowmeters. These comprise essentially :
(i) a primary device (e.g. Pitot or Venturi tube simple diaphragm orifice plates shaped nozzle) to set up a differential pressure and (ii) a differential pressure gauge (float diaphragm differential pressure oscillating ring balance or flow transmitters etc. type).
(2) Variable area (variable aperture) flowmeters. These usually consist of a graduated cone-shaped tube containing a heavy float which is carried along by the current until the flow of the liquid between the float and the wall reaches equilibrium. For high pressure liquids use is made either of magnetic flowmeters (the position of an iron float in a non-magnetic tube being shown externally by a magnet) or of valve flowmeters (an iris diaphragm fitted inside the tube being connected in parallel with a small flowmeter).
(3) Flowmeters which operate by using magnetic fields ultrasound or heat. This heading excludes :
(a) Hydrometric paddle-wheels for measuring the rate of flow in rivers canals etc. which fall in heading 90.15 as hydrological instruments.
(b) Apparatus which merely indicate the total amount of liquid delivered over a period which are classified as supply meters in heading 90.28.
(B) Anemometers of the special types used for recording the rate of flow of air currents in mines tunnels chimneys furnaces and conduits in general and consisting essentially of a bladed fan and a calibrated dial. In some devices the measured values are converted into electrical signals.
(II) INSTRUMENTS AND APPARATUS FOR MEASURING OR CHECKING THE LEVEL OF LIQUIDS OR GASES
Level indicators for liquids and indicators for the content of gasometers.
Level indicators for liquids include :
(1) Float-type. These may give a direct reading on a graduated column mounted on the float or the effect may be transmitted to a dial needle by means of a cable and drum or be converted into an electrical signal.
(2) Pneumatic and hydrostatic type. These are used to measure the level in pressure tanks by means of a differential pressure gauge.
(3) Two-colour light type for boilers. These are based on the difference in the refractive indices of water and steam. They consist of a set of lamps colouredscreens an optical system and a level which indicates in different colours therespective heights of the water and the steam.
(4) Electrical-type based for example on the variations of resistance capacitance ultrasound etc. This heading covers not only level indicators for closed reservoirs or tanks but also those for open basins and canals (hydroelectric works irrigation systems etc.). To ascertain the content of a gasometer the level of the " bell " is measured either directly or from a dial needle to which the bell is connected by means of a cable and drum. Instruments for measuring or checking the level of solid materials are excluded (heading 90.22 or 90.31 as the case may be).
(III) INSTRUMENTS AND APPARATUS FOR MEASURING OR CHECKING THE PRESSURE OF LIQUIDS OR GASES
Pressure gauges (e.g. manometers) apparatus for measuring the pressure of a liquid or gas. These differ from barometers in that the latter measure atmospheric pressure while pressure gauges indicate the pressure of a liquid or gas in a closed space. The main types of pressure gauges are as follows :
(1) Liquid-type pressure gauges (mercury water or other liquids or two non- miscible liquids). The liquid is contained in a glass or metal tube; these gauges may be of the single column type U-tube type inclined tube or multitube type or be in the form of an oscillating ring balance.
------------------------------------------------------------------------------