Within a plant or piping system, every process places different demands on equipment and valves. There is, therefore, a wide and extensive range of different designs and types available worldwide. The functionality, service life and safety of the plant, and not least the product quality produced, are therefore particularly dependent on the correct choice of valve, measurement and control components.
The way to choose the correct valve
In order to define the optimum device version for the intended use, a precise analysis of the operating parameters should, therefore, be carried out. The resulting profile of requirements is then used to select the optimum valve or equipment system from the versions available.
Analysis of the equipment requirements
Analysis of the requirements is divided into three categories:
- Procedural and process requirements
- Media influences
- Technical plant requirements
To ensure that none of the operating parameters and requirements is neglected and that potential economical factors are not overlooked, it is very helpful to record all criteria in writing. The selection diagram can also be used to select other components such as pumps, filters, sensors, etc.
Procedural and process requirements
Category 1: Determining the process parameters
- Operating and ambient temperature
- Operating pressure and pressure rating
- Volumetric flow (Kv value) and flow velocity
- Other performance requirements, e.g. mixing, distribution, control and regulating applications.
When determining these parameters, it is important that all operating conditions are taken into account. Frequently, attention is only given to the actual process. Working situations such as cleaning and/or sterilising a plant are often overlooked. However, completely different operating conditions may well come into play, which place much greater stresses on the pipework components than the actual plant operation, and which may well have a negative impact on the function and service life.
Category 2: Determining the media parameters
- Chemical properties (inert, corrosive, explosive)
- Mechanical properties (contaminants, particles, bubble formation, abrasion, viscosity)
- Electrical properties (conductivity, static charge)
- Aggregate state
The specific properties of the working media (fluids) must be examined with respect to all of their relevant physical and chemical properties. In addition, potential interaction, for example, between temperature, pressure or aggressivity based on concentration, should not be overlooked. Equally, the flow velocity has a direct effect on abrasion (including particle content) of the medium and/or formation of cavitation. It is always important to clarify the question: Is there only one working medium, or will the equipment be used for mixtures, compounds, cleaning agents, sterilisation media or other additives? Even the smallest addition of other substances can have a dramatic effect on the service life of the materials and the seals and gaskets.
Technical plant requirements
Category 3: Determining the existing and/or required plant design
- Required control function (manual, pneumatic/hydraulic, motorized, magnetic)
- Safety requirements (explosion protection, dangerous volatile substances, emergency function)
- Ambient conditions (cleanroom, hot/cold, dusty, vibration, chemical, damp, outdoors, saline and corrosive vapours => corrosive ambient conditions)
- Existing plant design (PLC, fieldbus/communication interfaces, control medium)
- Compliance with standards and regulatory codes
With an already existing plant or in established premises, numerous factors must be taken into account. However, also in a new building, various parameters already exist. Typical examples include control technology for installed component actuators (compressed air connections present or not) or level of plant automation (feedback/control via PLC required or not). Also, mobile solutions, predominantly in water treatment, determine various parameters, for example, normally only manual or motorized actuators can be used in this instance.
Following precise analysis of the equipment requirements and other factors, the most suitable equipment can now be selected from an extensive product range. For this purpose, it should always be ensured that the provider also has a corresponding wide range of products and versions. If this is not the case, there is always the risk that the wrong equipment or an unsuitable device will be recommended due to limited availability. Where possible, accessories should come from the same product range. Alternatives to this are accessories that have already proven their compatibility with the same device in a plant.
Optimization of the selected equipment
Once the valve has been defined, a further step must be carried out. In addition to the "standard version", many valve manufacturers offer additional sub-versions, which offer an excellent performance profile. GEMÜ, for example, offers multiple body/seat and actuator sizes for a connection size. Among other things, this helps to prevent unwanted physical phenomena such as cavitation and to reduce operating costs. For example, the use of smaller actuator sizes based on a more cost-effective user profile can save energy during operation (keyword: Oversizing)
Based on the operating parameters and the application conditions, there are normally a number of solution approaches. The technically best variant of a valve is often – in our experience – also relatively expensive. Therefore, plant engineers and operators also want to consider the "second best" type. This normally also satisfies all the requirements but may come up against its limits when it comes to service life and functionality.
Cost benefit analysis
When selecting the latter, the "second best" solution approach, it is important at a later point in time to analyse whether, in fact, this offers the most cost effective solution. If for example, a material is less resistant to a medium and the valve body has to be replaced at close intervals (servicing costs, installation time), it may be more cost effective to change to another, technically superior material.
If in doubt or to get assistance in selecting the correct valve contact Gemu Australia to speak with applications and valve specialist.