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A sampling valve is a type of
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
used in process industries that allows taking a representative portion of a
fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
( gases,
liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, ...
s, fluidized,
solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...
s, or slurries) to test (e.g. by physical measurements, chemical analysis, microbiological examination), typically for the purposes of identification, quality control, or regulatory assessment. It is a
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
used for sampling. The sampling valve allows the operator to extract a sample of the product from the production line or reactor and safely store it for transportation to the laboratory where it will be analysed or to the archive room where it can be retrieved for further use. In
chemical plant A chemical plant is an industrial process plant that manufactures (or otherwise processes) chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transfo ...
s, a sample can be taken during the process to ensure that the output meets specifications (or that the quality is acceptable), before shipping the chemical good or before accepting the chemical product.


Sampling problem

When sampling chemical products, it is of utmost importance to select representative material to analyse. The sample must be representative of the lot, and the choice of samples is critical to producing a valid analysis. The statistics of the sampling process are also important.The University of Adelaide, Department of Chemistr
"Sampling"
/ref> And in order for a sample to be representative, it must not contain remains of previous batches that might have stay in the valve's "dead space". For example, a
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve ...
commonly found in tap valves consists of a ball that control the flow of the liquid. Once the valve is closed, liquid stays in the ball and the next time the valve is opened, that liquid flows first. If a sample is taken using a ball valve, the valve has to be flushed before the sample is taken. This raises two additional problems: # If the liquid is a chemical substance that solidifies at room temperature such as
polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
or other plastics, it can block the valve and prevent a second sample to be taken. # The residue of the chemical substance that was flushed needs to be recycled or destroyed at a cost both for the chemical plant and the environment. When sampling hazardous chemicals or deadly substances, it is important that the operator is not exposed to toxic fumes or vapours. These can fatally harm people and should they be released in the atmosphere, they will pollute the environment.


Choosing a sample valve

When choosing a sampling valve, different factors have to be considered: * The material, pressure and temperature rating, gaskets, size and position of the valve according to the
pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circular ...
specification of the plant. * The handle or actuator type according to the position (reach) of the valve and according to the sampled chemical (e.g. whether if the product contains solid particles or not) * The receptacle to store the sample for transportation (bottles, container, bag, piston injector or syringe)


See also

* Other type of
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
s * Sampling


References

{{Reflist Valves