A sampling valve is a type of valve used in process industries that allows taking a representative portion of a fluid (gases, liquids, fluidity, solids, 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 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 analyzed or to the archive room where it can be retrieved for further use.
In chemical plants, 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.
This article contains the following:
Sampling problem
Choosing a sampling valve
Sampling Valve Applications
1. 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.
And in order for a sample to be representative, it must not contain remains of previous batches that might have stay in the sampling valve's "dead space". For example, a ball valve commonly found in tap valves consists of a ball that control the flow of the liquid. Once the sampling valve is closed, liquid stays in the ball and the next time the sampling valve is opened, that liquid flows first. If a sample is taken using a ball valve, the sampling 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 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 extremely important that the operator is not exposed to toxic fumes or vapour. These can fatally harm people and should they be released in the atmosphere, they will pollute the environment.
2. 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 sampling valve according to the pipe specification of the plant.
The handle or actuator type according to the position (reach) of the sampling valve and depending of the chemical to sample (i.e. if the product contains solid particle or not)
The receptacle to store the sample for transportation (bottles, container, bag, piston injector or syringe)
3. Sampling Valve Applications
The sampling valves are most commonly used to simplify the extraction of samples from or the injection into tanks, reactors, or pipelines and allow for trouble free service over long periods of time. SchuF has a variant for whatever process element is most important for your application, whether it be fire safety, ease of maintenance, high temperature, or zero leakage, or a combination of all elements.
Many of sampling valves are exclusive designs for specific custom applications. They are widely used in the Refinery, Pharmaceutical, Fine Chemicals, Biochemical, Plastics and Polymer industries.
