Choke valve

Choke valve

A Choke valve is a type of valve designed to create choked flow in a fluid. Over a wide range of valve settings the flow through the valve can be understood by ignoring the viscosity of the fluid passing through the valve; the rate of flow is determined only by the ambient pressure on the upstream side of the valve.

In automotive contexts, a choke valve modifies the air pressure in the intake manifold of an internal combustion engine, thereby altering the ratio of fuel and air quantity entering the engine. Choke valves are generally used in naturally aspirated engines with carburetors, to supply a richer fuel mixture when starting the engine. Most choke valves in engines are butterfly valves mounted in the manifold above the carburetor jet, to produce a higher partial vacuum and thereby draw more fuel into the intake stream.

In heavy industrial or fluid engineering contexts, a choke valve is a particular design of valve that raises and lowers a solid cylinder (called a "plug" or "stem") which is placed around or inside another cylinder that has holes or slots. The design of a choke valve means fluids flowing through the cage are coming from all sides and that the streams of flow (through the holes or slots) collide with each other at the center of the cage cylinder, thereby dissipating the energy of the fluid through "flow impingement". The main advantage of choke valves is that they can be designed to be totally linear in their flow rate.

Automotive

A choke valve is sometimes installed in the carburetor of internal combustion engines. Its purpose is to restrict the flow of air, thereby enriching the fuel-air mixture while starting the engine. Depending on engine design and application, the valve can be activated manually by the operator of the engine (via a lever or pull handle) or automatically by a temperature-sensitive mechanism called an autochoke.

Choke valves are important for normally aspirated gasoline engines because small droplets of gasoline do not evaporate well within a cold engine. By restricting the flow of air into the throat of the carburetor, the choke valve reduces the pressure inside the throat, which causes a proportionally greater amount of fuel to be pushed from the main jet into the combustion chamber during cold-running operation. Once the engine is warm (from combustion), opening the choke valve restores the carburetor to normal operation, supplying fuel and air in the correct stoichiometric ratio for clean, efficient combustion.

Note that the term "choke" is applied to the carburetor's enrichment device even when it works by a totally different method. Commonly SU carburetors have "chokes" that work by lowering the fuel jet to a narrower part of the needle. Some others work by introducing an additional fuel route to the constant depression chamber.

Chokes were nearly universal in automobiles until fuel injection began to supplant carburetors. Choke valves are still common in other internal-combustion applications, including most small portable engines, motorcycles, small propeller-driven airplanes, riding lawn mowers, and normally aspirated marine engines.

Industrial

Heavy duty industrial choke valves control the flow to a certain Flow Coefficient (Cv) determined by how far the valve is opened. They are regularly used in the oil industry and for highly erosive and corrosive purposes, they are often made of tungsten carbide or inconel.

External links


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • choke valve — In a carburetor, it is the choke butterfly …   Dictionary of automotive terms

  • Choke — may refer to: Choking, obstruction of airflow into the lungs Choke (horse), a condition in horses in which the esophagus is blocked Choking game, a schoolyard game involving deprivation of oxygen to the brain Chokehold, a grappling hold performed …   Wikipedia

  • Valve — This article is about the flow control device. For the game developer, see Valve Corporation. For the electronic component, see Vacuum tube. For other uses, see Valve (disambiguation). These water valves are operated by handles. A valve is a… …   Wikipedia

  • valve — A device used to either open or close an opening to allow or prevent the flow of a liquid or gas from one place to another. There are many different types. See ABS relay valve accumultor valve air valve carburetor air control valve air gulp valve …   Dictionary of automotive terms

  • choke kick — A preset position for the choke valve set by manifold vacuum that is routed through a carburetor body passage to the choke diaphragm …   Dictionary of automotive terms

  • choke — [chōk] vt. choked, choking [ME choken, aphetic < OE vt. aceocian, to choke, prob. < base of ceoke, jaw, CHEEK] 1. to prevent from breathing by blocking the windpipe or squeezing the throat of; strangle; suffocate; smother; stifle 2. to… …   English World dictionary

  • choke — (v.) c.1300, aphetic of acheken (c.1200), from O.E. aceocian to choke (with intensive a ), probably from root of ceoke jaw, cheek. Related: Choked; choking. The noun is recorded from 1560s. Meaning valve which controls air to a carburetor first… …   Etymology dictionary

  • choke — ► VERB 1) prevent (someone) from breathing by constricting or obstructing the throat or depriving of air. 2) have trouble breathing. 3) (often be choked with) fill (a space) so as to hinder movement. 4) make speechless with strong emotion. ► NOUN …   English terms dictionary

  • choke — A butterfly valve or plate located near the top of the carburetor that limits or restricts the amount of air allowed to enter the carburetor, thus enriching the fuel air mixture and enabling the vehicle to start and run more easily when cold.… …   Dictionary of automotive terms

  • choke — 1. v. & n. v. 1 tr. hinder or impede the breathing of (a person or animal) esp. by constricting the windpipe or (of gas, smoke, etc.) by being unbreathable. 2 intr. suffer a hindrance or stoppage of breath. 3 tr. & intr. make or become speechless …   Useful english dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”