The truth about valves

The truth about valves

Stricter regulations, increased cost of shutdown periods and higher output standards have seen valves become one of the most important aspects of any manufacturing or process plant. A millilitre too much or too little of a chemical, flow shutting off a second too late or the failure of a valve operation could have disastrous consequences for the plant operator, public and the environment. As a result, pipework and valve manufacturers are constantly receiving enquiries about the installation, performance and effects of manual and actuated valve packages.

Geoff Rogers, our valves manager, tells us about the most frequently asked questions that are received by the in-house valves department relating to the use of valves in industrial applications.

What is the most suitable valve for flow control? Typically, a diaphragm valve is considered in relation to flow control, however a metering ball valve will offer a more linear control of flow. In many valves the flow increase is greater or smaller at either the start or the end of the opening cycle, but a metering ball valve is linear throughout the full cycle, making it ideal for flow control applications.

Can a diaphragm valve be installed in an automatic control application? Yes, a diaphragm valve can be installed in automatic control applications by using a pneumatic actuator with a 3 to 15psi control pressure or 4-20ma on an electro-pneumatic control head. Using a Programmable Logic Controller (PLC) also allows the flow to be controlled.

How can you tell if a manual valve is open / closed in a computer controlled pipework system? Ball valves can be fitted with a switch box that can send a signal to a Programmable Logic Controller (PLC) on the status of the valve. This can be installed using an additional mounting kit.

Which types of valves are most suitable when dosing small quantities? It is important to have a valve with an instant shut off so that over-dosing does not occur. Therefore, when dealing with small volumes, Solenoid valves are ideal; the valve is controlled by an electric current through a solenoid, offering fast and safe control.

Which type of valve is suitable for fluids containing debris / solids in suspension? A diaphragm valve is very forgiving as the rubber seal flexes around the object. As the areas are smooth, there is nowhere for the debris to become lodged. Sediment strainers are also available if small amounts of foreign bodies need to be removed from the liquid.

How can you stop a pump running dry? By using a non-return valve, such as a ball check valve, in conjunction with an electronic flow switch on the inlet side of the pump to stop the fluid siphoning back and retaining it within the pump. This means excessive wear caused by dry running is kept to a minimum, therefore extending the life of the pump.

What is meant by the term ‘fully lugged’ when referring to a butterfly valve? Fully lugged valves have threaded inserts moulded into the valve body, enabling the valve to be fitted at the end of the pipeline using only one flange, and leaving the other end of the valve open.

In large diameters (over 2”/ 63mm), what is the difference between ball and butterfly valves? Butterfly valves are more compact and so are ideal for valves that need to be fitted in confined spaces. In large sizes, the flow can also help to close the valve, making it easier to operate. A ball valve has a full bore so the flow is not restricted however, in a large flow, a ball valve can be difficult to close as the ball generates higher levels of friction.

What is the difference between L-port and T-port 3-way valves? L-port valves are usually used to divert flow and, with the optional turn limiter, can be engineered to never shut off the flow. A T-port valve has more flow options but at least two ports are always open.

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