V A L V E S
an expert point of view

Most Common Mistakes While Specifying The Valves.

As the old saying goes, “If you have enough time to do same thing over & again, you have enough time to do it right the first time.”

Today business moves in a highly accelerated rate; particularly in the process industries. Customers often consider Valves as less-priority item and do not order in the initial procurement stage while ordering other equipment. They demand the product to be shipped overnight, spending exorbitant amounts of money on priority freight cost such as AIR, Courier etc. In an effort to accommodate the customer’s urgent request, most of the sales people do not check application for which the product will be used.

It is logical that all parties involved should ask few simple questions to prevent the mistakes that can lead to disaster in a flow control system.

The Application : many possibilities!

“Take Ball Valves, for example; can be used for ON/OFF application as well as REGULATING application”. Unless the user indicate the specific application, the valve may not perform properly if used on wrong application. The soft seat when exposed repeatedly for regulating flow in semi open position, the seat will erode faster; SS encasing to be provided for such service.

Simple question to ask : What is the application; on/off or regulating?

Hot and cold!!

Often it is noticed that working temperature is not indicated while specifying the valve. As long as the customer has ordered metal seated valves such as Gate/Globe/Check the same will suffice. However, in case of soft seated valves such as Diaphragm/Butterfly/Ball/Plug etc. it is essential to indicate the working temperature as the soft seat has a specific temperature limitation beyond which the seat failure is eventual.

Simple question to ask : What is the working temperature?

Rating is not always the pressure!!!

Generally piping class ratings are given a pressure rating while specifying a valve, for example, ANSI #150. Although majority of the valves are designed to suit the piping pressure rating, few types such as Diaphragm, Butterfly etc. with elastomer seat are designed for reduced non-shocking pressures. No doubt they are suitable to mount between ANSI #150 flanges but the pressure cannot comply to ANSI #150. It is therefore advisable that working pressure is indicate while specifying the valves so that correct type can be offered; else there could be multiple problems and failure of the process system.

Simple question to ask : What is the working pressure?

Sometimes to Pass you have to “Fail”!!!!

Many times customers and engineers ask or specify “Pneumatic Valves” without mentioning the “type of action”. Invariably manufacturers land up quoting a standard actuator; say a “Double Acting”, but this may create problems at a later stage as the instrumentation engineers would expect a START/STOP of the flow in case of fail close or fail open actions; but would never get!!!!

It is therefore essentially required to specify the type of action for the pneumatic operated valves. The options can be : FAIL CLOSE (NORMALLY CLOSED),
FAIL OPEN (NORMALLY OPEN), DOUBLE ACTING (STAY AS IS).

It is also recommended to check with the manufacturer for the air pressure that will be required in order to operate the valves and choose the coned actuator size.

Simple question to ask : What is the type of Actuator and fail position?

Mis-interpretation!!!!!

Solenoid valves are often misapplied as well. Generally, a solenoid valve is required to default to a desired position, referred to as fail-safe, upon loss of power. Even the relatively universal “energize to open” is occasionally mis-ordered as “normally open.” In some of these cases, the process control system will compensate for the one valve operating improperly, but in the event of a power loss, the results might be disastrous.

Simple question to ask : What is the function of Solenoid Valve?

Irreconcilable Differences : Media and Material!!!!!!

Material compatibility is critical to the safe operation of a system and personnel safety. The result of a material misapplication can be catastrophic. Corroding pipes and valves can cause chemical leak, which may harm the workmen, cause productivity losses and affect various other pollution and environmental norms. Additional expenses for clean up of the chemical spills and fines may also be expected.

Proper material compatibility analysis requires knowledge of the type, concentration, pressure and temperature of fluid(s) being handled to select an appropriate valve body and seal material. Every materials manufacturer publishes an easy to use chemical resistance guide which takes the guess work out of specifying compatible materials. Unfortunately, anxious designers are notorious far ignoring the published pressure-temperature ratings for the valve and seal materials, assuming that they all have a built in safety factor.

Simple question to ask : What is the operating fluid data?

Size Matters………….. But Sometimes Pressure Matters More!!!!!!!

If the pipe diameter is 2”, most people assume that a 2” valve will do the job. In a few cases, that’s true; but in general, pressure considerations are of utmost importance in a piping system and therefore critical when specifying a valve.

Outlet pressure, for example, is critical to solenoid valves but frequently overlooked. If downstream pressure sufficiently exceeds the valve’s outlet pressure rating, the core spring may not be powerful enough to close the valve.

Simple question to ask : What is the inlet, outlet & differential pressure?

The Autobahn in Disguise!!!!!!!!

Velocity is very often overlooked when specifying a valve. Unlike that famous European roadway, a piping system does have a “speed limit.” The generally accepted safe velocity for a thermoplastic piping system is 5 feet/second. But like the pace of today’s business environment, a “slow” 5 ft/second process system just isn’t productive enough! Unfortunately, it is becoming the rare exception to the rule.

At higher velocities, such as an ultra-pure water system in a semiconductor lab facility, an improperly selected valve can easily create a water hammer situation if it closes too quickly. This dangerous energy surge travels at the speed of sound and frequently causes damage to pipes, fittings, valves and instrumentation.

The problems of this nature can be prevented with a little planning; always consider liquid velocity, and valve closing time.

Simple question to ask : What is the fluid velocity?

Letting the Electric Slide!!!!!!!!!

Neglect of actuator voltages and electrical enclosure types is not quite as common as the mistakes above; but often creates the most headaches and is potentially the most dangerous.

If an incorrect voltage is specified on a solenoid valve or a valve actuated by an electric motor, it will not operate properly. Often the actuator or coil will overheat, and may cause a fire.

Ratings on electrically actuated valves are designed to provide for safety. NEMA has ratings for many types of electrical enclosures for a variety of environments. Most common are general purpose, water tight, corrosion resistant and explosion proof. Specifying the wrong enclosure type may endanger personnel and property.

Simple question to ask : What is the line voltage?

Review

Too often, valves are purchased by pipe size and without enough consideration for pressure, flow, chemical compatibility, performance, or safety factors. The mistakes listed above are just the most common-and most obvious. To properly specify the valve, all components and aspects of the system should be taken into consideration.

For more information on selecting the right valve for your application contact:

BDK ENGINEERNG INDUSTRIES LTD.
47/48, GOKUL ROAD, HUBLI – 580 030, KARNATAKA-INDIA
PHONE : 0836-2331499/2333930 FAX : 0836-2330799 / 2330899
EMAIL : bdkhubli@bdkindia.com WEBSITE : www.bdkindia.com