Where should control valves be installed?

Valves

Before installing a control valve it is necessary to ensure that the size, pressure rating, materials and end connections are all suitable for the conditions under which the valve is expected to work.

The company is the world’s best Self-operated type control valve supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

All reputable manufacturers of automatic control equipment will provide detailed instructions covering the correct installation procedure for their equipment. Data will also be provided on how to set up the equipment, plus any routine and regular maintenance to be undertaken. In most cases, the manufacturer will also offer an on-site commissioning service. In some cases, a regular after-sales maintenance contract can be agreed. Module 5.5 covers the major points to be considered before installation.

Piping upstream and downstream of the control valve should be clear and unobstructed. The correct operation of a valve will be impaired if it is subject to line distortion stresses. It is important to ensure that all flanged joints are square and true and that pipework is adequately supported.

Control valves should generally be installed in horizontal pipelines with the spindles vertical.

Pipework systems will often be subjected to pressure testing prior to use. This test may be carried out at a pressure above the normal working conditions. It is necessary to ensure that the control valve and its internals are designed to withstand this higher test pressure.

Control valves are essentially instruments and will be damaged if dirt or other abrasive or obstructive materials are allowed to enter them. It is essential in most applications to prevent this by fitting pipeline strainers upstream of any control valve.

Valves must also be accessible for routine maintenance, such as re-packing of glands and the replacement of internals. To facilitate this sort of work, isolating valves of a full bore pattern either side of the valve will keep plant downtime to a minimum while the work is carried out.

If a plant must be kept in operation at all times, even when a control valve is being inspected or maintained, it may be necessary to fit a valved bypass. However, the valve used in the bypass must be of good quality and should either be a characterised throttling valve or another control valve of the correct Kvs. Any leakage through it during normal operation will affect the action of the control system. It is not recommended that manual bypasses be fitted under any circumstances. The control valve must be installed to ensure the correct direction of flow of the medium passing through the valve. Usually a ‘direction of flow’ arrow is cast into the body of the control valve. The valve must have a suitable flow capacity and incur an acceptable pressure drop.

In steam lines, it is important to provide a steam separator and/or a trapping point upstream of the valve, as shown in Figure 5.5.1. This will prevent the carryover of condensate through the control valve, which would otherwise reduce its service life. This drain point is also important if the control valve is likely to remain closed for any length of time. If a condensate drain is not fitted, waterhammer and potentially serious damage can result when the valve opens. The provision of a steam separator and strainer ensures good steam conditioning.

Looking for control valve installation best practices?

Below we'll cover 7 things you must do when installing a high pressure control valve. 

1. Don't Hold the Control Valve by the Tubing

Tubing often looks like the perfect handle to lift a valve. However, lifting the valve by this method can quickly bend the tubing itself or the connection point where the nut and ferrell are. And if you bend it too much it can break that seal to the valve. 

The best way to pick up a control valve is either by the valve body itself, the topworks or the lifting hooks on the top.

2. Install Isolation Ball Valves 

The second best practice is to install ball valves on both the upstream and downstream side of the control valve. 

When it's time to do maintenance on a valve, you will need completely cut off any pressure on the upstream and downstream side. This process is referred to as the double block and bleed procedure, and ball valves make it easy to do.

3. Mount the Control Valve Vertically 

We often get asked if customers can mount their through-body control valve sideways.

Normally for a through-body valve, the inlet and outlet piping should be horizontal.

Want more information on double seated control valve? Feel free to contact us.

However, sometimes, depending on construction of the vessel, the piping the valve is to be installed on is vertical, so if you install the valve without adjusting the piping, the valve would be sideways.

We do not recommend you do this. Here's why.

If you mount the valve horizontally, the weight of the topworks internals and the valve trim pushes the valve stem onto one side of the packing. Because of this, over time you will experience premature wear on the packing and valve stem that could potentially lead to leaks in the valve.

Mounting a HPCV sideways does not allow the lubricating oil on the topworks to travel to the stem. This expedites the wear on the upper stem.

The best practice is to install the valve in vertical orientation so it looks like it's standing upright.

4. Check the Fail Position

Check and make sure the fail position of the control valve is correct for your application. 

The easiest way to do this is to look at the position indicator to see if the valve is open or closed before you have any pressure on it. 

Is it open? Then it's set to fail open. 

Is it closed? Then it's set to fail closed. 

The good new is if it's in the wrong fail position, you can open up the top works and convert it without having to buy extra parts.

5. Check for Clean, Dry Supply Gas

Wet or dirty gas doesn't always affect the valve itself, but it does affect the pilot or level controller communicating with it. And if device is not working, the control valve won't work properly. 

Examine the vent port of the control device (pilot or liquid level controller). If the vent port looks like it has dirt stuck around it, your supply gas is probably wet. After exhausting the wet gas, dirt will begin to stick to the moisture. 

If this is the case, move your tubing to pull supply gas from a high and dry spot or consider using compressed air for instrument supply. 

6. Use the Star Pattern to Tighten Flange Connection 

When installing a control valve with a flanged connection, tighten the bolts in a star pattern, just like you do on a car wheel. 

One side cinched down too much doesn't create a good seal. Also, any time you are replacing a flanged valve, make sure to replace the flange gaskets. Using a damaged flange gasket can lead to issues.

7. On a Threaded Valve, Use Sealant

When installing a valve with a threaded connection, use Teflon tape or pipe dope (or both) on the threads. This helps seal the connection to prevent leaking and protects the threads. 

To speak with an expert about more control valve installation best practices, contact your local Kimray store or authorized distributor.

Are you interested in learning more about Control valves for chemical ethylene refining? Contact us today to secure an expert consultation!