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Regulating valve (CV3000)

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The new moon was published in 065438+1October 19. Read at 23:56 in 2007 (9) Comments (0)

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0 regulating valve

I. Introduction

1. Basic concepts

A. control valve (IEC-control valve: a terminal element formed by a power-operated device in an industrial process control system, which includes a valve with a component for changing the flow rate of process fluid, and the valve is connected with one or more actuators. The actuator is used to respond to the signal sent by the control element) to accept the control signal of the regulator and realize the automatic control of the process fluid.

B flow coefficient kv(cv)- water (H2O) with a temperature of 5-40℃(60℉) drops at a pressure of 0. 1MPa( 1psi), and the cubic meter (American gallon/minute) flowing through the control valve within1h.

C. Liquid pressure recovery coefficient (FL)- a function of the internal geometry of the valve body, which represents the measured value of the conversion of kinetic energy into pressure energy after the minimum contraction cross section of the fluid.

Non-blocking flow: fl = √ (p1-p2)/(p1-PVC)

When blocking the flow: FL = √ (p1-p2) max/(p1-ffpv)

The smaller the resistance, the smaller the FL and the more serious the pressure recovery.

D pressure difference ratio coefficient (XT) —— When the flow is blocked, the pressure difference ratio X(⊿P/P 1)=XTK/ 1.4.

Reaching the limit value is called critical pressure difference ratio. XT—— Differential pressure ratio coefficient

E. flow obstruction-when the inlet pressure of the valve remains constant, the outlet pressure gradually decreases. When the pressure difference increases, the flow cannot be further increased, that is, the flow increases to the maximum limit. At this time, the flow state-flow is blocked.

F. Contraction cross section-the cross section with minimum flow after throttling of the valve.

G. pressure recovery-the phenomenon that the fluid has the highest velocity and the lowest pressure in the contraction section, and then the velocity gradually decreases, the pressure gradually increases, and the pressure rises-pressure recovery.

H cavitation-when the fluid flows through the regulating valve, the pressure in the contraction section reaches the saturated vapor pressure at the inlet temperature, and bubbles appear. Then, due to the pressure recovery, the bubble will burst. The whole process from bubble formation to bubble rupture-cavitation.

First, flash evaporation-when the fluid flows through the regulating valve, bubbles are generated due to the pressure drop to the saturated vapor pressure, but when the downstream pressure is equal to or lower than the saturated vapor pressure at the inlet temperature, the bubbles cannot be broken and flow out of the regulating valve with the liquid. This process is flash evaporation.

2. Development of control valve

1). In the 1920s, control valves came out.

2). In 1960s, China carried out standardization and standardized design-seven series, including-P.N.S.Q.W.R.T. 。

3). The 1970s. Eccentric rotary valve. Sleeve valve.

4). The 1980s. Imported technology-cv 3000.

5). The 1990s. High performance, specialization and intelligence.

6) .265438+20th century. Smart. Fieldbus)-① Technology-① Remote diagnosis, ② Remote adjustment, ③ Single-ended detection, ④ High reliability.

3. Composition of control valve

4. Selection of control valve

Two. Form of regulating valve body

1. Single seat control valve

-Features: 1. The leakage rate is low. IV-0.0 1% coefficient of variation, V-0.00 1% coefficient of variation, VI-0.0000 1%.

2. Unbalanced shaft thrust is large and δ P is low. 3. Simple structure.

-Application: 1. Optimization of cleaning solution. 2. Small caliber (below 1B). 3. Low leakage rate.

4. The switch is cut off. 5. Low δ P, standard executing agency.

2. Cage control valve

-Features: 1. The leakage rate is high. II-0.5% coefficient of variation, III-0. 1% coefficient of variation, VI-0.0000 1%.

2. Unbalanced shaft thrust is small and δ P is high.

3. Anti-cavitation, anti-corrosion and low noise.

4. Small pressure difference and good adjustment stability.

-Application: 1. The pressure difference is high and the pressure changes frequently. 2. The pressure difference is high, with slight cavitation and corrosion.

3. Cage single-seat regulating valve

-Features: 1. The leakage rate is low. Four -0.0 1%2. Unbalanced shaft thrust is large and δ P is low.

3. Two-stage depressurization to avoid cavitation.

Application: Water with large pressure difference and high temperature produces cavitation and cavitation. δP≥3 MPa

4. Balanced cage single seat regulating valve

Features: 1. Single seat seal of pressure balance cage with piston ring.

2. Low leakage rate. III-0. 1% coefficient of variation, IV-0.0 1% coefficient of variation.

3. Unbalanced shaft thrust is small and δ P is high.

4. Small pressure difference and good adjustment stability.

Purpose: High pressure difference and low leakage rate to adjust and cut off exhaust conditions.

5. Low noise control valve

-Features: The sleeve is throttled by small holes to avoid vortex generated by high-pressure jet gas.

Valve vibration and high noise.

-Application: High pressure difference gas. δP≥ 1 MPa

6. Angle control valve

-Features: 1. The leakage rate is low. IV-0.0 1% coefficient of variation. Coefficient of variation V-0.00 1%, VI-0.0000 1%.

2. Unbalanced shaft thrust is large and δ P is low. 3. Simple process and self-cleaning function.

4. The valve body is not easy to be corroded.

-usage: 1. Pipeline requirements. 2. High viscosity. Slurry medium.

3. Due to the large pressure difference, the valve body is seriously corroded.

-Note: 1. The actuator needs to be enlarged when entering the side and leaving the bottom. 2. The bottom enters the side and exits, which is equivalent to a single-seat valve.

7. Three-way regulating valve

-Features: 1. One valve can replace two valves to realize shunt or confluence. 2. Low leakage rate. IV-0.05438+0% coefficient of variation. 3. Unbalanced shaft thrust is large and δ P is low. 4. Temperature difference δ t ≤ 150-200℃.

Application: heat exchanger, spraying conditions.

8. Heat preservation jacket regulating valve

9. Butterfly control valve

-Features: 1. Simple flow path, small pressure loss and large valve capacity. 2. The allowable pressure difference is very small.

3. Valve leakage: clearance type 2%CV, stepped valve seat 0. 1%CV, 0.0000 1%CV.

4. Inherent flow characteristics. ≈%.

-Application: 1. Low pressure difference and large flow. 2. Slurry medium. 3. Non-metallic lining is corrosion resistant.

10. Cam deflection control valve

-Features: 1. The valve has large capacity and adjustable transmission ratio. 2. The flow path is smooth, and impurities are not easy to precipitate.

3. Eccentric rotation has no friction, long sealing life, and the guide wing makes the fluid move.

Smooth adjustment and large allowable pressure difference. 4. Low leakage rate. 4 -0.0 1%.

Polytetrafluoroethylene-"0"

-Application: 1. Large capacity and wide adjustment range. 2. Mud fluid containing soft materials.

3. Switch off the working state. 4. Requirements of small size and light weight.

1 1.o-shaped stop ball valve

-Features: 1. Straight flow path, low flow resistance, large capacity and no impurity precipitation.

2. Low leakage rate. V-0.00 1%，VI-0.000 1%。

3. The allowable pressure difference is large and the adjustment range is large. 4. Concentric rotation, large friction and short service life.

-Purpose: Switch action to cut off working conditions.

12.v-shaped regulating ball valve

Features: 1. Low flow resistance, large capacity and no impurity precipitation. 2. Low leakage rate. V-0.00 1%，

VI-0.0000 1%。

3. The allowable pressure difference is large and the adjustment range is large. 4. Concentric rotation, large friction and short service life.

-usage: 1. Switching action, adjustment and cut-off conditions. 2. Slurry and fibrous media.

Comparison of regulating valve functions

Three. Calculation of CV value

1. Throttling principle and flow coefficient of control valve (Kv)

The energy loss of incompressible fluid flowing through the regulating valve is:

H=(P 1-P2)/rg ……( 1)

If the opening of the regulating valve is fixed and the fluid is incompressible, then R remains unchanged. Fluid per unit weight

The energy loss of is proportional to the kinetic energy of the fluid:

H= (V02/2g) ……(2) ( V0=√ (H*2g)/)

The average velocity of the fluid in the regulating valve is:

V0=Q/A ……(3) (Q=V0*A)

(1).(2).(3) Synthesize and get the flow equation of the regulating valve:

Q=A/√ { √ 2(P 1-P2)/r }……(4)

(4) Substitution unit:

Q = {5.09a/√} {√△ p/r} m3/h，Kv = 5.09a/√。

Q=Kv√△P/r

Kv=Q√r/△P =5.09A/√

R- fluid density -t/m3. Gravity acceleration. -Resistance coefficient of control valve.

A- The cross-sectional area of the control valve connecting pipe is cm2. △P=P 1-P2 100kPa。

Q- Volume flow of fluid, m3/h

CV value calculation formula:

1. Incompressible fluid (liquid)

Thermodynamic critical pressure Pc and critical temperature Tc of some substances

2. Compressible fluid (gas) average gravity method Ym(FCI)

3. Water vapor

Compressible fluid (gas) expansion coefficient method (y)(IEC)

Steam expansion coefficient method (y)(IEC)

Binomial Flow Expansion Coefficient Method (y)(IEC)

Liquid and non-liquefied gases: Effective density method (Ye) is adopted.

Binomial Flow Expansion Coefficient Method (y)(IEC)

Liquid and vapor: Binomial density method (Ym) is adopted.

Symbols and units

Z- compressibility-is a function of specific pressure and specific temperature.

Pressure recovery characteristic parameters of control valve

Four. flow characteristic

2. Choose:

1. Incompressible fluid (liquid)

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