How do I select a control valve?

Select a control valve in nine stages: collect process data, calculate the required Cv or Kv, check for choked flow, flashing and cavitation, choose the valve body type, choose the flow characteristic, specify pressure class and materials, select the actuator and fail position, verify performance, then complete the specification sheet. Bore size follows from the calculated Cv, not from the pipe size.

How is Cv calculated for a control valve?

Cv is the US liquid flow coefficient: the flow in US gallons per minute that produces a 1 psi pressure drop across the valve at fully open with water at about 60 degrees Fahrenheit. For liquids, Cv = 1.96 x Ft x Q divided by N x Fl x Fp x the square root of (P1 minus P2), where Q is flow in gpm, N is the number of flow paths, P1 and P2 are upstream and downstream pressure in psia, and Ft, Fl and Fp are temperature, liquid recovery and piping geometry correction factors.

What is the difference between Cv and Kv?

Cv and Kv measure the same flow capability in different units. Cv uses US gallons per minute at a 1 psi drop, Kv uses cubic metres per hour at a 1 bar drop. Kv is approximately equal to 0.865 times Cv, and Cv is approximately equal to 1.156 times Kv.

What is the difference between linear and equal percentage flow characteristics?

A linear trim has a constant slope, so 50 percent of rated travel gives roughly 50 percent of rated flow. An equal percentage trim has a constant proportional change, so 50 percent travel gives about 50 percent of rated Cv. Use linear trim when process gain is constant, and equal percentage trim when pressure drop or system resistance varies, which is the most common case.

What does ATO and ATC mean on a fail-safe actuator?

ATO means air to open, so loss of air supply closes the valve and the valve fails closed. ATC means air to close, so loss of air supply opens the valve and the valve fails open. Pneumatic spring-return actuators are ATO or ATC as standard. Electric actuators achieve fail position through a return spring, a stored-energy mechanism, or a battery or UPS backed drive.

Should a control valve be sized for maximum flow?

Not necessarily. A valve sized only for peak flow spends most of its life near 10 percent open, where the trim sees high velocity, noise, vibration and rapid wear. Target steady operation between about 20 and 80 percent of rated travel. If maximum flow is rare, consider a split-range arrangement, two valves in parallel, or an interchangeable trim.

How do I prevent cavitation in a control valve?

Cavitation occurs when vapour bubbles form and collapse in the throat. Control it by keeping downstream pressure above the fluid vapour pressure, reducing the pressure drop across a single stage, using multi-stage or staged trim, specifying an anti-cavitation cage, selecting a larger bore and trimming the flow so velocity stays low, and avoiding high recovery factors downstream of the valve.

What is valve rangeability?

Rangeability is the ratio of maximum to minimum controllable Cv. A conventional globe valve typically offers 30 to 50 to 1, while characterized trim can reach 100 to 1 or more. Practically, most process control loops need a turndown of only about 30 to 1 between the minimum controllable and maximum rated stroke.

LAPAR Control Valve

Professional manufacturer of globe control valves, ball control valves, butterfly control valves , self control regulators and special control valves for your specific application.

What are control valves?

Control valves are final control element in automatic control terminology that are used to manage and control fluid flow, pressure, temperature, or liquid level by varying the flow passage size. In process systems of production wells, oil and gas plants, Chemical and Petrochemical industries, refineries, and power plants, Control valves are frequently used to control or manage any of the process parameters. You can choose the correct control valve for the specific desired pressure, control valves can automatically do the job and eliminate the need for you to constantly keep an eye on the system.

Control valve selection

Why Lapar Control Valve?

Over 30 years of professional experience in manufacturing control valves, with patented technology, mature and stable products, and considerate service.

Our competitive advantage:

Consistent product quality and reduction of defective rate
Improved manufacturing process and better productivity
Significant cost reduction versus competitors

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How to Select a Control Valve?

Control Valve Selection: A 9-Step Guide to Sizing, Trim, Materials and Fail-Safe Actuation

Selecting a control valve is a chain of dependent decisions: the process data fixes the Cv, the Cv fixes the bore, the bore constrains the trim, and the trim constrains the material. This guide walks the whole chain in the order an engineer should actually work, and flags the mistakes that show up most often in failed selections.

SIZING YOUR VALVE NOW!

What products and services can we offer?

Our portfolio is built around on/off isolation valves, control valves and actuation units engineered for the thermal power, chemical, water, oil and natural gas industries. Alongside standard supply, we provide value-added services including bespoke special-product manufacture and field maintenance and repair.

Isolation Valves

Control Valves

Customization Services

Control Valves, Ball Valves, Butterfly Valves, Globe Valves, Gate Valves, Non Return Valves

Who is using Lapar's Control Valves?

Lapar from Italy is a professional manufacturer of industrial valves provides performance, safety and long service life products which have to reliably handle the most aggressive of substances, our products stand the test of time in food & beverage, water & wastewater, ultra pure water, desalination, chemical, textile, transportation, pharmaceutical, pulp & paper, mining, boiler and power industries.

Sturdy Construction

The control valves are fully standardized in design to ensure structural consistency and durability.

High Efficiency

The Control valves manufacturing standing on user experience, operation in simple and high efficiency.

Mature Experience

Our control valves have been widely used in petroleum, chemical, power, food and other industries for many years.

Continuous Service

Lapar's control valves optimize cost and performance, significant cost reduction versus competitors.

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Address: Galleria del Corso 1, Milano (MI), Italy
Postcode: 20122
Phone: +39 02 8200.0500
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Website: https://www.valveu.com