The key to valve longevity is the observation of a handful of practices, some of which are the products of common sense but others of which you might find surprising. When properly maintained, valve efficiency is achieved long after installation.

First, it is important to understand the material the valve is made of as well as any directions that may be marked upon it. Basically, the valve should be made of the same material as the pipe system to which it is attached. Piping material is chosen specifically for the purpose of the system and the manner of fluid that it controls. This material choice is based on a host of factors including the corrosiveness, abrasiveness and contaminant level of the fluid. For the same reasons, any valve installed in the system should be of a consistent material.

As far as any markings on the valve are concerned, in addition to the manufacturer's name there is usually a basic service rating. It is important that the plant manager be able to read these service ratings because they denote the levels at which each valve can be used safely. In addition, arrows are oftentimes cast on the valve to indicate the preferred direction of flow. It should go without saying that the directions marked on the valve should be heeded.

In-plant inspection upon valve receipt is a good habit to undertake. This ensures that no damage occurs while the valves were in transit. Key areas to focus on include inspecting the valve ends, the pressure-retaining shell and any valve operating mechanisms. As for storing the intact valves once they have arrived, plant managers should see to it that they are kept in a clean storage area, far from any areas in which dust and grit are present. Any protective covers for the valves should be kept on them until they are ready to be installed. Also, whether the valve disk is shipped to the user in an open or closed position, it should be kept in this same position until the time of installation. And, of course, before any valve is attached to the system it should be properly cleaned with either compressed air or water.

A simple precaution plant managers can take that will lengthen the lifetime of the valve tenfold, is to leave a sufficient amount of space between packing rings on valve glands. The manufacturer's instructions might advise the installer to do otherwise, sometimes suggesting that the packing rings should be placed together end-to-end. This arrangement reduces the life span of both the valve and pump. It stands to reason that manufacturers would suggest this method since they stand to sell more packing if it needs to be replaced frequently. When packing rings are packed end-to-end, they tend to move down the sacrificial sleeve of the shaft, chafing at the material as they do so. This chafing occurs because when the packing rings expand and contract (as they would normally do in the course of operation), they have no room to adjust and so, therefore, have to push themselves along the shaft. The friction that is created heats the lubricating agent and causes it to lose its lubricity. This condition of poor lubrication causes a braking effect that results in extra loading on the driver unit that, in turn, causes more energy to be used in the system than is necessary. Ultimately, this translates into higher operational and maintenance costs. Leaving a 1/16 gap between the packing ring butts can circumvent this frustrating scenario and allow the packing to operate up to ten times longer.

Keep in mind that the operational success of any valve gland lies in how it is initially packed. Each ring must be cut on a mandrel before being set squarely in the stuffing box, and each subsequent ring should be installed on the gland by turning it towards a different quarter of a clock-face. In other words, the first ring should be installed at the 12 o'clock position, the second at the 6 o'clock position, the third at the 3 o'clock position, the fourth at 9 o'clock and so on, repeating this for as often as there are rings. For glands with only three rings, the rings should be installed in the same way but by spacing them each a third of a clock-face apart.

Considerable care should be exercised in regards to globe valves whose bonnets are held in place with a large nut. Basically, be sure that the nut remains tight when the valve is opened hard against the back seat. Loosening of the nut is likely to occur if a wrench or valve cheater bar is used to open the valve. If a situation does arise that absolutely calls for the valve to be opened with one of these tools, unless there is a large pressure differential across the seat, the valve should be replaced immediately.

Finally, steps should be taken to ensure that the valves are installed correctly to begin with. This entails the proper alignment of the piping system before the valve is even put in place. Valves should not be added to an unaligned piping system in hopes that it will tighten the pipes and pull them into place. This arrangement causes undue stress to be exerted upon the valve, hampering its correct functioning and seriously shortening its span of usefulness. It is of the greatest importance that all valves, as well as the pipes to which they are connected, are in proper alignment at the time of installation.

Remember, without valves there would be no way to control either the flow or temperature of the fluid in a piping system. When treated like the essential devices that they are, valves will provide a higher level of performance for a longer amount of time.

Source: Improving Valve Life and Operating Efficiency the Easy Way
John C. Robertson
Maintenance Resources, Reference Library
http://www.maintenanceresources.com/ReferenceLibrary/ezine/valves.htm