CORDOBA, ARGENTINA--August 18, 2008--Researched by Industrial Info Resources (Sugar Land, Texas)--On August 11, Valero Energy Corporation (NYSE:VLO) (San Antonio, Texas) shut down the 65,000-barrel-per-day (BBL/d) light gas-oil distillate hydrotreater (D2) at the company's San Nicolas refinery in Aruba because of a broken valve. The 42,000-BBL/d Visbreaker unit, which was shut down on July 22 because of a problem in its main tower as well as fissure issues, remains offline and under maintenance.

Now valves are widely used in our life. You can find them in anywhere. Sometimes they play a important place in some special place. And the broken of valves may cause serious consequences. So the maintenance of valves is very important.

In fact all valves require proper care and maintenance, as does other more complex equipment, to ensure they are kept in optimum working order. Valves that remain in one position for a long period could end up becoming inoperable. Many factory maintenance engineers overlook valves because of the daunting prospect of going through the large number of those components in any one facility.

The principle difficulties encountered with valves are leakage past the seat and disk, leakage at the stuffing box, sticking valve stems, and loose valve disks. Losses due to leakage that is not corrected mount up considerably over time. For example, over a period of a month, a small 1/32 inch hole would waste 69.552 cubic feet of air at 100 psi, 3,175 pounds of steam at 100 psi, or 4,800 gallons of fuel at 40 psi. The ABF should know how to prevent and correct these faults.

Valve leakage, generally caused by failure of the disk and the seat to make close contact, may result from any of the following: —Foreign substances, such as scale, dirt, or heavy grease lodged on the valve seat may prevent the disk from being properly seated. —Scoring of the valve seat or disk, this may be caused by erosion or by attempts to close the valve on dirt or scale, results in leakage. —A warped disk may result if the guides fit too tightly, if the spindle guide is bent, or if the valve stem is bent. Using a valve disk or body that is too weak for the purpose for which it is used permits distortion of the disk or seat under pressure.

So if you want to ensure valves work properly when needed the valve maintenance should be carried out regularly to. A good way to get a handle on this task is to create a valve schedule. The schedule can just be a simple spreadsheet and should contain information like valve tag numbers, purpose of the valve, location of the valve, size and type of valve, and a reference to a drawing. The schedule will be a useful aid for mechanics to locate the valves and could also help to speed finding the right valves to operate in an emergency. It takes a little time to gather the information the first time, but it will be well worth the effort.

A regular valve maintenance program will extend the life of valves, allow predictive and preventive maintenance, and ensure minimal problems when the valves are needed.