Valve Basic Concepts at http://www.valvias.com/basic.php

Basic Concepts

What is a valve?

A valve is a mechanical device which regulate either the flow or the pressure of the fluid. Its function can be stopping or starting the flow, controlling flow rate, diverting flow, preventing back flow, controlling pressure, or relieving pressure. Basically, the valve is an assembly of a body with connection to the pipe and some elements with a sealing functionality that are operated by an actuator. The valve can be also complemented whit several devices such as positioners, transductors, pressure regulators, etc.

General: Fluid Basics

Basic Concepts > General > Fluid Basics  

Concepts

Flow Coefficient CV and Kv

Flow Coefficient comparative

Flow coefficient for ball valve

Flow coefficient for butterfly valve

Discharge Coefficient

Reynolds Number

Flow Equations - Online Calculation

Flow Coefficient (Cv and Kv)

Pressure drop Coefficient zeta (ζ)

Discharge Coefficient (C)

Flow Rate (Q)

Flow velocity (v)

Head drop (Δh)

Pressure drop (ΔP)

Cavitation Number

Flow Coefficient Definition When flow goes through a valve or any other restricting device it loses some energy. The flow coefficient is a designing factor which relates head drop (Δh) or pressure drop (ΔP) across the valve with the flow rate (Q)

( equation for liquids only)

Q: Flow rate/ ΔP: Pressure Drop / Sg: Specific gravity (1 for water)/ K: Flow coefficient Kv or Cv

Go to online calculation of the Flow coefficient Cv and Kv

Each valve has its own flow coefficient. This depends on how the valve has been designed to let the flow going through the valve. Therefore, the main differences between different flow coefficients come from the type of valve, and of course the opening position of the valve.

Flow coefficient is important in order to select the best valve for a specific application. If the valve is going to be most of the time opened, probably there should be selected a valve with low head loss in order to save energy. Or if it is needed a control valve, the range of coefficients for the different opening positions of the valve should fit the requirements of the application.

At same flow rate, higher flow coefficient means lower drop pressure across the valve.

Depending of manufacturer, type of valve, application the flow coefficient can be expressed in several ways. The coefficient can be non-dimensional or with units if parameters such as diameter or density are considered inside the coefficient or just in the equation.

Most of valve industry have standardized the flow coefficient (K). It is referenced for water at a specific temperature, and flow rate and drop pressure units. Same model valve has different coefficient for each diameter.

Kv is the flow coefficient in metric units. It is defined as the flow rate in cubic meters per hour [m3/h] of water at a temperature of 16º celsius with a pressure drop across the valve of 1 bar.Cv is the flow coefficient in imperial units. It is defined as the flow rate in US Gallons per minute [gpm] of water at a temperature of 60º fahrenheit with a pressure drop across the valve of 1 psi.

Kv = 0.865 · Cv or Cv = 1,156 · Kv

(Equivalence between flow coefficients Kv and Cv)

At valves which discharge the flow directly into the environment it is used the non-dimensional Discharge Coefficient(C).

Types of Valves at http://www.valvias.com/types-of-valves.php

Valves can be classified by:

The operative of the valve closure member

The kind of closure member movement defines both the geometry and operative of the valve.

• Multi-turn valve (linear motion valves): The closure member has a linear displacement generally by turning its threaded stem several times.This operation is slow, but it gives accuracy and stability to position the closure member, which is necessary in some control valves.Types of valves: Gate valve, Globe valve, Fixed cone valve, Needle valve and Pinch valve. • Quarter-turn valve (rotary valve): The closure member as well its shaft turn 0º-90º; from the fully-open position to the fully-closed position. They are quick opening/closure valves.Types of valves: Ball valve, Butterfly valve, Plug valve, Spherical valve.

The functionality of the valve

• Control: pressure / flow rate regulation.

• Closure at over-speed flow. (i.e. immediate closure if downstream pipeline is broken by accident).

• Overpressure protection.

• Back flow prevention (check valve).

• On/Off service.

The nature and physical conditions of the flow

• Low/High temperatures.

• Low/High pressures.

• Cavitation risk.

• Corrosive or erosive properties of the flow.

• Viscosity: Gas, liquid, solid.

• Hygiene requirements (for the food or pharmacy industry...).

• Explosion and risk of inflammability (chemical, petrochemical industry).

Other forms of valve classification

• Admissible leakage level.

• Connection to the pipe.

• An unique direction of the flow or bidirectional flow.

• Number of ports: most of the valves have two port, named inlet and outlet port. But for same applications there are multi-port configured valves. They can be three-way and four-way valves.

• Angle between the inlet and outlet port of the valve.

Types of Actuators at http://www.valvias.com/types-of-actuators.php

Actuators for valves can be classified up several characteristics:

By the type of movement

Multi-turn. Quarter-turn. Linear. Lever.

By the energy source

Manual Electric: they can be drived by direct and alternate current. Pneumatic: they use pressured air or gas to create motion. They are widely used in the industry due

to their low cost. In case of failure they are easy to diagnose or repair in field, rather than electric actuators.

Oleo-Hydraulic

Functionality

On / Off valve service Positioning to % open Modulating to control changes on flow conditions Emergency Shut Down (ESD)

Other characteristics

Explosion-proof Safety integrity level (SIL) Enclosure: IP and NEMA.

Types of Actuators

Manual Actuator (Gearbox)

Pneumatic Diaphragm Linear actuator

Pneumatic Diaphragm Rotary actuator

  

Standard Regulators at http://www.valvias.com/standard-regulators.php

Norms & Test

Standard Regulators

Valve Standards

Actuator Standards

Management Standards

INTRASTAT code and Taric

Instituts, organizations and regulators for standards in the field of valves and actuators:

ABNT Associaçao Brasileira de Normas Técnicas

ANSI American National Standards Institute

API American Petroleum Institute

ASTM American Society for Testing and Materials

AWWA American Water Works Association

CEN European Comittee for Standardization

DIN Deutsches Institut für Normung

DODSSP - Department of Defense Single Stock Point for Mil Specs and Standards

IAPMO International Association of Plumbing and Mechanical Officials

IECC International Electrotechnical Commission

ISO International Organization for Standardization

JSA Japanese Standards Association

KSA Korean Standards Association

MSS Manufacturers Standardization Society

ON Österreichische Normungsinstitut

SAI Standards Australia International

UL Underwriters Laboratories