The two key questions to select a hydraulic valve

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By Matt Clift (Director of Global Product Management & Marketing)

In terms of variety of product options to choose from, hydraulic valves have some of the widest array of options to choose from. There are quite literally hundreds of different configurations possible!

However, it doesn&#;t need to be complex. In this article of our Know More, Grow More series, we will simplify the process and will present the two primary questions you need to ask when selecting a hydraulic valve.

As a reminder, for more information about selecting the right valve, or in fact any product in your drip irrigation system, make sure you check out Module 2 of Rivulis Knowledge Hub.

 

 

Selecting the right valve type may seem complex, but it becomes straightforward by answering two key questions:

• What is the valve&#;s primary function?
• How will the valve be operated or controlled?

Question 1: What is the Primary Function of the Valve?

The first question focuses on the primary function, or "what the valve does." There are nine different primary functions for hydraulic valve as follows:

• Basic: A valve body without any accessories, often used by growers and dealers who wish to build their own valves. 

• On/Off: This valve is either on or off, with no pressure regulation or flow control since there is no pilot. Ideal for simple in-field operation and small farms without automation.
• Pressure Reducing (PR): Reduces downstream pressure for consistent water pressure, and subsequent uniformity in each block regardless of upstream pressure fluctuations. The majority of valves are PR valves in most irrigation systems.

• Pressure Sustaining (PS): Maintains upstream pressure, important for components such as filters that require a minimum pressure for back-flush.
• Pressure Reducing & Pressure Sustaining (PR/PS): Combines both functions, eliminating the need for two separate valves.
• Electric Control: Controls valve opening through electric automation, allowing remote operation.
• Quick Relief: Acts as a safety valve by relieving system pressure above a preset value. Unlike PR valves, quick relief valves are for quickly expelling excess pressure when spikes occur.
• Flow Control: Restricts flow to a determined rate. These are different to PR valves as the valves restrict to a specific flow through differential pressure. An example of use is to restrict the flow of back-flush discharge from a media filter during flushing.
• Level Control: Opens and closes valves based on set tank points, useful for maintaining storage water levels.

Question 2: How Will the Valve be Controlled?

We now know what the valve will do. The second question addresses how the valve will be operated. There are three main options:

• Manual: Involves a ball valve for manual operation. Often remotely controlled valves will have a manual override added to the valve in addition.

• Hydraulic: Utilizes water pressure transferred through a hydraulic tube to control the valve&#;s diaphragm via a hydraulic relay. 

• Electric: Uses a solenoid where current through a wire creates a magnetic field that moves the piston.

 

 

By answering two questions above, you streamline the process of selecting the right hydraulic valve for your system.

Next Steps

Once you have determined the primary function and control method of your valve, the next steps involve specifying the valve's parameters and accessories:

• Material: Choose between plastic or metal based on your application. Plastic valves are lighter, more economical, and corrosion-resistant. Metal valves are necessary for higher pressure and larger size applications.
• Size: Choose the size based on the required flow and head loss. This is chosen according to the needs of your system&#;s hydraulic design.
• Connection Type: Select the connection type according to your region (standard for your country) and application need (flange, thread, etc).
• Pilots: Are chosen to the pressure regulating requirement of the hydraulic design and the system components.
• Throttling: Controls how much a valve can open. It does not regulate pressure, i.e. it does not respond to pressure variations. It only puts a limit on how much the valve can open.
• Solenoids: Are available in a wide range of variations, and your selection will depend upon your control system and valve application.

Dive deeper about hydraulic valve selection in the Valves Section on the Rivulis Knowledge Hub, or download Book 2 for the complete guide for drip irrigation component product selection.

Read more about Rivulis&#;s hydraulic valve product offering in the valve section on rivulis.com.

Please note. This article is provided as a high level overview only. It is important that you verify what is best for your specific application, including for design, installation, operation, and maintenance. For both personal and irrigation system protection and before use, it is important to read the relevant suppliers&#; instructions (for non-Rivulis products such as pumps, chemicals, fertilizers, etc), to consult with applicable professionals, and to read the relevant section of the Rivulis Drip Guide/Knowledge Hub, particularly with respect to safety and handling information, and more detailed instructions for use.

Additional resources:
Understanding Calcium Carbide Uses in Welding Applications

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Industrial valves are crucial components in most industrial processes. According to Allied Market Research, the demand for industrial valves is expected to grow considerably, reaching a market size of $110.5 billion by . In , the market size was valued at $65 billion.

One of the most common industrial valves is PVC (polyvinyl chloride) valves. PVC valves are widespread in the chemical industry, often the preferred choice because of their excellent resistance to corrosion from most of the chemicals used in industrial processes.

However, you must know which PVC valve will best suit your application. Critical factors that you should consider when selecting a PVC valve include operating pressure and temperature, corrosion, operation mode, ease of maintenance, and types of seals and ends.

Here&#;s what you need to know about PVC valves and how to select the best one for your industrial chemical application.

Why PVC Material Works for Chemical Processing

PVC and CPVC (chlorinated polyvinyl chloride) are common choices of material for industrial valves. PVC and CPVC industrial valves are more affordable and resistant to corrosion from various bases, acids, and salt solutions.

However, PVC can be corroded by moderately polar solvents such as tetrahydrofuran. It&#;s still resistant to solvents at either end of the polarity scale, including fuel, water, and oil. These are the more generally encountered everyday chemicals.

CPVC offers extra chemical resistance, albeit at a slightly higher cost than PVC. CPVC valves are made by increasing the chlorine content in PVC from ~57% to ~67-74%. Therefore, CPVC valves can be used in broader applications.

CPVC valves are also suitable for higher temperatures, getting up to F to F for some applications and products. PVC is often rated for a maximum temperature of F if the pressure and chemical exposure are favorable.

PVC also offers good fire resistance, though CPVC offers superior resistance.

PVC has ~50% more density than PP and HDPE. The greater density gives it strength advantages over other common types of plastic. HDPE pipe walls often have to be 2.5 times thicker than PVC to support the same pressure at room temperature for water applications.

You also get better flexural and tensile strength from PVC than from PP (polypropelyne) or HDPE (high-density polyethylene.

The Risk of CPVC Softening

Despite CPVC often being more resistant than PVC, it is prone to softening if used to transport solvents like ethers, ketones, alcohols, esters, and aromatics.

These chemicals can be absorbed in the piping, softening the structure. This softening can eventually lead to ductile rupture or other damages.

CPVC softening can still happen if the piping or valve is exposed to these chemicals in its environment, despite not transporting them.

What to Consider When Selecting PVC Valves for Chemical Processing

Whether using a PVC or CPVC industrial valve option, here are the critical factors to consider.

Temperature and Pressure

Industrial PVC valves are rated based on the maximum pressure and temperature they can take in the process. A few essential questions to ask to establish the correct rating include:

• The maximum pressure of the chemical process
• The upstream flow of the fluid between the source and the valve
• The downstream flow of the fluid after it leaves the valve
• The maximum fluid temperature

The combined fluid temperature and pressure of the process should not exceed the valve&#;s published rating per the manufacturer. The pressure and temperature ratings for PVC industrial valves vary depending on the valve body and trim material combination, body shell, seal material, and end connections.

The rating selected should be sufficient under these combinations to handle the maximum possible process temperatures and pressure.

Corrosion

Corrosion will determine whether a PVC or CPVC valve will be the most suitable choice for an industrial chemical process. CPVC valves offer more resistance to corrosion than PVC valves. Therefore, they might be the better choice depending on the application.

The corrosive effects of the chemicals a plant uses on PVC or CPVC should be assessed to determine the most suitable industrial valve for the chemical process.

If the valve is not resistant to corrosion, it can lead to contamination of the fluid media, leaks, and valve failure. Corrosion of industrial valves can also pose a significant safety risk to humans working close to the plumbing.

Seals and Ends

The material making the PVC valve seals and ends is crucial in determining the type of valve most suitable. There is a selection of plastic and elastomeric seals, diaphragms, and liners based on their chemical compatibility with the fluid used in the process.

Elastomeric seals made from natural and synthetic rubber offer the best sealing characteristics. However, plastics such as perfluoroalkoxy alkane (PFA) and polytetrafluoroethylene (PTFE) provide better resistance to harsh chemicals.

Most manufacturers offer a chemical resistance guide that can be a good resource to help you select the suitable seal material.

The valve ends should also be considered in terms of:

• Their pressure and temperature rating
• Compliance with industry and plant standards
• The seal welding used
• The installation and maintenance cost

Mode of Operation

The mode of operation or actuation required for the PVC valve should be considered. The most common considerations that will affect the type of valve chosen include the following:

• Will the valve need manual or automatic actuation?
• Will the actuator be hydraulic, electric, or pneumatic?
• Will the valve operator be oval, lockout type, or deadman?

Automated valves using electric, pneumatic, or hydraulic actuators should produce enough force to overcome the valve&#;s static friction and dynamic torque. Manufacturers often supply valve torque requirements based on the pressure drop across the valve.

A safety factor of 10-20% is often added to ensure the reliable operation of the actuators.

Ease of Maintenance

The choice of PVC industrial valve should be easy to maintain. Ease of maintenance is crucial for application stability and valve reliability.

For instance, ball valves are resistant to jamming, clogging, or malfunctioning. However, they shouldn&#;t be used for flow adjustment and control. Under such usage, they can easily leak and fail prematurely.

The valve connection types will also affect the ease and speed of maintenance. For instance, threaded ends are easy and cheap to install but are more prone to stripping and leaking. Welded ends are rigid and leak-tight but expensive to repair and replace since the whole valve needs to be cut out of the line.

Contributing Author: Mark Ligon, Marketing Manager, Commercial Industrial Supply

Mark Ligon is the marketing manager at Commercial Industrial Supply, a supplier of commercial & industrial piping, fittings, valves, filtration products and accessories. Ligon enjoys educating businesses on the specific parts of piping systems so managers can make informed decisions. 

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