What is cavitation in instrumentation?

Cavitation is the formation and collapse of vapor bubbles (cavities) in the liquid flowstreams caused by changes in pressure and velocity. There are four primary negative side effects of uncontrolled cavitation in control valves: high noise, excessive vibration, material damage, and deterioration of flow effectiveness.

What is cavitation in control valves?

Definition. Cavitation in control valves occurs only with liquid flows—gases cannot cavitate. Vapor bubbles form if the liquid's pressure falls to near the vapor pressure as the liquid passes through the control valve. Bubbles can suddenly collapse or implode as the pressure increases down line, producing cavitation.

What is cavitation and flashing?

Flashing is an in- to- out event while cavitation is an out- to- in event. Flashing occurs at low pressure and cavitation occurs when the low-pressure bubbles collapse at the high-pressure region within the pump casing producing a shock wave. Reduction of volume of the vapor sphere concentrates matter and energy.

How is cavitation formed?

cavitation, formation of vapour bubbles within a liquid at low-pressure regions that occur in places where the liquid has been accelerated to high velocities, as in the operation of centrifugal pumps, water turbines, and marine propellers.

How do you control cavitation and flashing?

What is Valve Cavitation? (Animation)

What causes cavitation in valves?

Cavitation happens in control valves when there's variation in the flow velocity, in particular, when the fluid in the valve accelerates rapidly. It occurs when the pressure drop in the valve exceeds a critical point or when downstream pressure exceeds the fluid vapor pressure.

What is control valve sizing?

The process of “control valve sizing” is a procedure where the dynamics of the system are matched to the performance characteristics of the valve. This produces a control valve of an appropriate size and type that will best meet the needs of managing flow within the process system.

What are the types of cavitation?

Two principal types of cavitation exist: vaporous and gaseous.

What is cavitation in mechanical engineering?

Cavitation is the formation of vapor phase cavities, or bubbles, within a liquid, usually due to rapid changes in localized pressure. Various mechanical parts such as pumps, control valves and propellers can cause cavitation to occur.

Where is cavitation used?

Cavitation bubbles are now used in a remarkable range of surgical and medical procedures, for example to emulsify tissue (most commonly in cataract surgery or in lithotripsy procedures for the reduction of kidney and gall stones) or to manipulate the DNA in individual cells.

What is critical pressure in control valve?

At this point, the steam velocity will be sonic and the flow area is at a minimum. The steam pressure at this minimum flow area or 'throat' is described as the 'critical pressure', and the ratio of this pressure to the initial (absolute) pressure is found to be close to 0.58 when saturated steam is passing.

What is flashing in pipes?

Pipe flashing, sometimes referred to as a roof boot, is manufactured to seal tightly around small ventilation pipes, plumbing, and other vents and equipment that protrude from the roof of a home or commercial building. The base is typically a flexible metal so that it is compatible with virtually any roofing material.

What is flashing in a valve?

Flashing occurs when liquid flows through a control valve and vaporizes, remaining a vapor. Flashing shares some common features with choked flow and cavitation in that the process begins with vaporization of the liquid in the vicinity of the vena contracta.

How do you calculate cavitation in a control valve?

The cavitation coefficient K_c is the ratio between the valve pressure drop at which cavitation starts and the difference between the inlet and the vapor pressure of the application. The allowable maximum ∆p before cavitation begins is ∆p = K_c (p₁ – p_v).

Can cavitation occur in valves?

Cavitation can occur in valves when used in throttling or modulating service. Cavitation is the sudden vaporization and violent condensation of a liquid downstream of the valve due to localized low pressure zones.

How do you calculate cavitation number?

The value of the cavitation number, i.e. CN = (p₁ − p_v)/(p₁ − p₂), determines the extent of the region that is filled with vapour inside the nozzle.

What is priming and cavitation?

Pump priming. Pump Cavitation. Basic. It is the process of filling liquid into the suction side, pump casing, up to the delivery valve. It is the effects of the bubble formation at the suction side that carries further to the pump inside and burst, causes damage to the impeller as well as the pump.

What is cavitation in centrifugal pumps?

Cavitation occurs in centrifugal pumps when the Nett Positive Suction Head Available (NPSHa) is lower than the Nett Positive Suction Head Required (NPSHr) causing the formation and accumulation of bubbles around the impeller eye that then collapse resulting in a series of mini implosions and significant damage to both ...

What is cavitation in Venturi meter?

The cavitating venturi is using to provide constant mass flow rate of liquid which is passing through a passage, independent of downstream pressure changes. The flow rate is a function of the upstream pressure, the throat area, the density and saturation pressure of the liquid.

What is cavitation effect?

Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid.

What is cavitation frequency?

Cavitation and Radio Frequency (RF) Body Shaping is a noninvasive procedure that uses low frequency sound waves that allows your body to break down stubborn fat deposits which then are metabolized and removed naturally through your body's filtration system.

How can cavitation be prevented?

What is FL and xT in control valve?

ANSI/ISA liquid sizing Equations use a pressure recovery factor, FL, to calcu- late the ∆Pch at which choked flow is assumed for sizing purposes. For compressible fluids, a terminal pressure drop ratio, xT, similarly describes the choked pressure drop for a specific valve.

What is the KV value of a valve?

The Kv-value is a measure of the flow rate through a valve for a given medium and pressure drop. The larger this value, the higher the flow rate through the valve will be at a given pressure drop. Usually, the Kv-value is given in the product description or datasheet.

How do you calculate Cv flow?

The equation for calculating the valve flow coefficient is Cv = Q √ (SQ/P).