05282017Sun
Last updateFri, 26 May 2017 2pm

i

The Future of Coal: Efficiency Over Politics?

The Future of Coal: Efficiency Over Politics?

Many changes in the power industry have ...

Valve World Americas Event Set for June 20-21

Valve World Americas Event Set for June 20-21

End users, distributors, EPC/AEC personn...

Water Hammer

Water Hammer

Water hammer is a shock wave transmitted...

Turning the Tables on Valve Corrosion

Turning the Tables on Valve Corrosion

Multiple valve manufacturers and users w...

Subscribe vmspr17

FREE SUBSCRIPTION*

•  Print magazine
•  Digital magazine
•  VALVE eNews
Read the latest issue

*to qualified valve professionals in the U.S./Canada

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

Advertisement
i

Industry Headlines

Emerson Acquires MYNAH Technologies

3 DAYS AGO

Emerson has completed the purchase of MYNAH Technologies, a long-time Emerson alliance partner. The addition of MYNAH will help support Emerson Automation Solutions and its Operational Certainty program. Terms of  the acquisition were not disclosed.

MYNAH software is currently in use at more than ...

Readmore

Roger Fix Named Chairman of Flowserve

4 DAYS AGO

In its most recent annual meeting, Flowserve announced that Bill Rusnack and Lynn Elsenhans have retired as members of the board of directors. Flowserve also announced that board member Roger Fix has been elected to replace Rusnack as chairman.

"Bill and Lynn provided years of distinguished service to ...

Readmore

Oil-Fired Plants Provide Small Amount of U.S. Electric Capacity, Generation

2 DAYS AGO

According to the U.S. Energy Information Administration , roughly 70% of petroleum-fired electric generating capacity that still exists today was constructed prior to 1980. Utility-scale generators that reported petroleum as their primary fuel comprised only 3% of total electric generating capacity at...

Readmore

ExxonMobil, SABIC Agree on Proposed Petrochemical Project

4 DAYS AGO

Affiliates of Exxon Mobil and SABIC (Saudi Basic Industries Corporation) signed an agreement to conduct a detailed study of the proposed Gulf Coast Growth Ventures project in Texas and begin planning for front-end engineering and design work. The agreement was signed during the Saudi-US CEO Forum in R...

Readmore

Kansas City Fed Manufacturing Survey Shows Expansion in May

1 DAY AGO

Tenth District manufacturing activity continued to expand at a moderate pace in May, and expectations for future activity increased strongly. Price indexes were mixed, but recorded little change overall. The month-over-month composite index was 8 in May, up from 7 in April but down from 20 in March.

Ac...

Readmore

Business Borrowing for Capital Investment Up 8% in April

2 DAYS AGO

The Equipment Leasing and Finance Association’s (ELFA) Monthly Leasing and Finance Index, which reports economic activity from 25 companies representing a cross section of the $1 trillion equipment finance sector, showed their overall new business volume for April was $7.9 billion, up 8% year-ov...

Readmore

Selection Considerations for Control Valves vs. Regulators

In any control system, the option potentially exists to select either a control valve or a regulator, so it is useful to compare the respective performance and economics of these approaches to arrive at some general selection guidelines.

Unlike regulators, control valves are not standalone products. A control valve is the final control element in a control system and needs to be evaluated in that context. A control valve is most frequently used in the control of the following parameters: temperature, pressure, flow and level.

However, in principle, any continuously varying system parameter that can be measured and compared to a set point can be controlled. Also, keep in mind that regardless of the parameter being controlled (the controlled variable), the control valve itself can only change the flow rate.

All control is to a set point, and the control system can be diagrammatically illustrated as shown in Figure 1.

spr09_bv_fig1

The essential feature of the controller (whether acting as a single-loop controller or as a component within a PLC or within a DCS or fieldbus device) is the incorporation of proportional and integral control modes capable of returning the measured variable to the set point following load changes or system disturbances. Control is generally within 5%, often within 1 to 2%.

Rising stem control valves are typically globe valves commonly used to the 2-inch size. However, globe valves can extend to at least 24 inches in size with special trims and cages for severe service and high-noise applications.

For economic reasons, rotary control valves are generally applied as line sizes increase above 2 inches and a variety of ball valves, eccentric plug and segmented ball valves, and butterfly valves exist in this segment of the market. The segmented ball valve is used in many applications and the largest size rotary control valves, such as butterfly valves, can extend to 72 inches in diameter.

Globe-style valves offer advantages in that the plug and/or cage can be more readily characterized to optimize the installed flow characteristic. Most rotary valves have an inherent flow coefficient characteristic that increases approximately exponentially with the increase in travel.

Although a range of actuators can be used, pneumatic actuation predominates. The diaphragm actuator is generally the style of choice due to minimized resistance and hysteresis for small changes in travel associated with control to within 1 to 2%. For improved control and minimized deadband, positioners are generally specified. It is also common practice for the current-to-pneumatic conversion to occur at the positioner. There is also a continuing increase in the use of intelligent or smart positioners, thereby providing automatic commissioning, higher accuracy, tight shut off, customizable characteristics and diagnostic capabilities.

There are obvious economic considerations associated with the choice of a control valve, which, at a minimum, require the incorporation of sensors and transmitters, controllers, positioners, instrument valves, tubing, wiring, calibration, tuning, etc. Generalized cost estimates can only be considered representative, at best, and can vary significantly depending upon application, size, material, accuracy and commercial circumstances.

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association