What is the difference between valve flow coefficient Cv and metric Kv?

Cv represents the flow of water in US gallons per minute (gpm) at 60°F through the valve with a pressure drop of 1 psi. Kv represents the flow rate in cubic meters per hour (m³/h) of water at 5-40°C with a pressure drop of 1 bar. The conversion relationship is Cv = 1.156 × Kv (or Kv = 0.865 × Cv).

Why are globe valves preferred over butterfly and ball valves for fine process regulation?

Globe valves offer superior precision, high rangeability (turndown up to 50:1), and customized cage/plug trims (equal percentage or linear) that eliminate abrupt throttling variations. Butterfly and quarter-turn ball valves have higher recovery factors and non-linear characteristics near low openings that make fine modulation prone to instability and cavitation.

What is the liquid pressure recovery factor FL?

The liquid pressure recovery factor (FL) characterizes the pressure recovery between the vena contracta and the valve outlet. A valve with a low FL (such as rotary ball or butterfly valves, FL ≈ 0.55 to 0.75) exhibits high internal pressure recovery and is significantly more vulnerable to cavitation and flashing than high-FL globe valves (FL ≈ 0.85 to 0.90).

Control valve types

Valve types and typical flow parameters

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Globe valves
Angle valves
Butterfly Valves
Gate Valves
Ball Valves

Top Sizing Tools

⚠️ ENGINEERING NOTICE & EDUCATIONAL DISCLAIMER: This interactive calculator is provided exclusively for preliminary estimation and educational purposes. It is not intended for detailed design or equipment procurement without certified vendor rating. No warranty, expressed or implied, is provided, and no liability is assumed.

Interactive Control Valve Sizing & Capacity Calculator

Calculate required \(C_v\) and \(K_v\), evaluate hydrodynamic velocity, verify pressure drop limits, and estimate butterfly valve capacities using the Midoux model.

Unit System: SI Metric (m³/h, bar, mm, m/s) US Customary (gpm, psi, in, ft/s)

Calculation Mode:

Volumetric Flow Rate Q [gpm]:

Valve Pressure Drop ΔP [psi]:

Specific Gravity (Water = 1.0):

Nominal Valve Size [in]:

Installed / Catalog Cv [gpm/psi^0.5]:

Opening Angle θ [degrees] (90° = fully open):

Calculation Outputs:

This page gives details about the mechanical design and hydrodynamic parameters of the main valve types found in chemical and process industries for control and regulation service. For detailed thermodynamic sizing formulas, please refer to the following companion guides:

Process Engineering Best Practices & Velocity Safety Rules

Liquid Flow Velocities: Keep valve port velocities below \(4.5\text{ m/s}\) (\(15\text{ ft/s}\)) and adjacent piping liquid velocities between \(1.0 - 2.5\text{ m/s}\) to prevent erosion, line vibration, and water hammer.
Allowable Sizing Margin: For stable control, size the valve so that normal operating flow corresponds to \(50\% - 70\%\) opening, and maximum flow does not exceed \(85\%\) of maximum rated capacity.
Cavitation & Flashing Check: Check the liquid pressure recovery factor \(F_L\). The maximum non-choked allowable differential pressure is: \[ \Delta P_{\text{allow}} = F_L^2 (P_1 - P_v) \] If \(\Delta P_{\text{actual}} > \Delta P_{\text{allow}}\), the valve operates in choked/cavitating flow. High-recovery valves (butterfly, ball, \(F_L \sim 0.55 - 0.75\)) are far more prone to cavitation damage than globe valves (\(F_L \sim 0.85 - 0.90\)).
Equal Percentage vs. Linear: Select equal percentage trims when valve pressure drop varies significantly with flow or constitutes less than \(40\%\) of total system friction. Use linear trims for level control or when valve pressure drop is nearly constant.

1. Globe valves

What is a globe valve ?

Globe valves are among the most popular designs for control valves as they allow fine throttling regulation that cannot be matched by standard butterfly valves, ball valves, or gate valves. The flow between the inlet and outlet is modulated by a moving plug that seals against an internal stationary ring seat.

They are named globe valves because of the globular shape of the cavities within the cast valve body.

Figure 1 : globe valve [Aimonen]

Figure 2 : globe valve [Padleckas]

1. body
2. ports
3. seat
4. stem
5. disc or plug (open position)
6. handle or handwheel
7. bonnet
8. packing
9. gland nut
10. fluid flow (open position)
11. Position of disc when valve is shut
12. Position of handwheel when valve is shut

The plug, cage, seat rings, and internal stems are collectively designated as the valve trim.

The drawings above represent the most common unguided/stem-guided globe valve. An alternative high-performance design utilizes a cylindrical cage inside the body. Lifting the plug within the cage exposes engineered characterized windows (slots or holes) that govern the flow versus lift relationship.

Flow parameters of globe valves

The values below are compiled from the Emerson Fisher Control Valve Handbook and provide typical values for preliminary process sizing:

Valve size (NPS)	Valve plug type	Flow characteristic	Port diameter (in)	Rated travel (in)	Cv	F_L	X_T	F_D
1/2	Post-Guided	Equal-Percentage	0.38	0.5	2.41	0.9	0.54	0.61
3/4	Post-Guided	Equal-Percentage	0.56	0.5	5.92	0.84	0.61	0.61
1	Micro-Form	Equal-Percentage	3/8	3/4	3.07	0.89	0.66	0.72
1	Micro-Form	Equal-Percentage	1/2	3/4	4.91	0.93	0.8	0.67
1	Micro-Form	Equal-Percentage	3/4	3/4	8.84	0.97	0.92	0.62
1	Cage guided	Linear	1-5/16	3/4	20.6	0.84	0.64	0.34
1	Cage guided	Equal-Percentage	1-5/16	3/4	17.2	0.88	0.67	0.38
1-1/2	Micro-Form	Equal-Percentage	3/8	3/4	3.2	0.84	0.65	0.72
1-1/2	Micro-Form	Equal-Percentage	1/2	3/4	5.18	0.91	0.71	0.67
1-1/2	Micro-Form	Equal-Percentage	3/4	3/4	10.2	0.92	0.8	0.62
1-1/2	Cage guided	Linear	1-7/8	3/4	39.2	0.82	0.66	0.34
1-1/2	Cage guided	Equal-Percentage	1-7/8	3/4	35.8	0.84	0.68	0.38
2	Cage guided	Linear	2-5/16	1-1/8	72.9	0.77	0.64	0.33
2	Cage guided	Equal-Percentage	2-5/16	1-1/8	59.7	0.85	0.69	0.31
3	Cage guided	Linear	3-7/16	1-1/2	148	0.82	0.62	0.3
3	Cage guided	Equal-Percentage	3-7/16	1-1/2	136	0.82	0.68	0.32
4	Cage guided	Linear	4-3/8	2	236	0.82	0.69	0.28
4	Cage guided	Equal-Percentage	4-3/8	2	224	0.82	0.72	0.28
6	Cage guided	Linear	7	2	433	0.84	0.74	0.28
6	Cage guided	Equal-Percentage	7	2	394	0.85	0.78	0.26
8	Cage guided	Linear	8	3	846	0.87	0.81	0.31
8	Cage guided	Equal-Percentage	8	3	818	0.86	0.81	0.26

Manufacturers of globe valves

For certified quotes, commercial sizing sheets, and pricing, refer to established globe valve manufacturers:

Guichon valves : http://guichon-vannes.com/
Sart Von Rohr valves : www.sart-von-rohr.fr
Gemu valves : gemu-group.com

2. Angle valves

What is an angle valve ?

An angle valve is a specialized variation of a globe valve where the inlet and outlet ports are configured at an angle of \(90^\circ\). This geometry provides an internal self-draining flow path with reduced impingement, making it ideal for slurry services, erosive fluids, coking hydrocarbons, and high pressure drop applications.

3. Butterfly valves

What is a butterfly valve ?

Figure 3 : Butterfly valve

Butterfly valves offer significant advantages in weight, space, and cost compared to globe valves. In the fully open position, they present very low resistance to fluid flow, enabling extremely high flow capacities (\(C_v\)) for compact pipe sizes.

However, standard butterfly valves provide less precise modulation, particularly near the closed position (\(< 20^\circ\) open) where torque dynamics and turbulence are high.

Sealing can be metallic (metal-to-metal, which permits minor leakage according to ANSI Class IV) or resilient elastomeric/PTFE lined for bubble-tight shut-off. In severe services, an eccentric or triple-offset high-performance butterfly valve is used, where the disc shaft is offset from the valve body centerline to eliminate seal rubbing and wear during rotation.

Figure 4 : eccentric butterfly valve

Flow parameters of butterfly valves

The values below are given by Emerson Fisher for standard 60-degree and 90-degree disc openings:

Valve size (NPS)	Degree of opening	Cv	F_L	X_T	F_D
2	60	58.9	0.76	0.5	0.49
2	90	80.2	0.71	0.44	0.7
3	60	115	0.81	0.46	0.49
3	90	237	0.64	0.28	0.7
4	60	270	0.69	0.32	0.49
4	90	499	0.53	0.19	0.7
6	60	664	0.66	0.33	0.49
6	90	1260	0.55	0.2	0.7
8	60	1160	0.66	0.31	0.49
8	90	2180	0.48	0.19	0.7
10	60	1670	0.66	0.38	0.49
10	90	3600	0.48	0.17	0.7
12	60	2500	-	-	0.49
12	90	5400	-	-	0.7
16	60	3870	0.69	0.4	-
16	90	8600	0.52	0.23	-

Midoux Empirical Model for Butterfly Valves

Alternatively, [Midoux] presents the following generalized hydrodynamic relations for butterfly valve capacity:

\[ \frac{C_v}{D_v^2} = 5 \times 10^{-2} \times f^2 \] \[ f = \frac{90 - \theta}{90} \] \[ F_L \approx 0.675 \]

Where:

\(D_v\) = nominal diameter of the valve \([\text{m}]\)
\(\theta\) = angle of closure / opening \([^\circ]\) (where \(f = 1\) represents the fully open \(90^\circ\) position)
\(C_v\) is calculated in \([\text{m}^3/\text{s}]\). Multiply by \(1.32 \times 10^6\) to convert to standard US gpm units (\([\text{gpm} / \sqrt{\text{psi}}]\)).

Worked Example (Midoux formula):

For a 4-inch valve (\(D_v = 0.1016\text{ m}\)) at fully open position (\(f = 1\)):

\[ C_v = 5 \times 10^{-2} \times (0.1016)^2 = 5.16 \times 10^{-4} \text{ m}^3/\text{s} \] \[ C_v = 5.16 \times 10^{-4} \times (1.32 \times 10^6) = 681 \text{ gpm} \] \[ F_L = 0.675 \]

This theoretical estimate aligns closely with experimental catalog data (NPS 4 catalog \(C_v = 499\), \(F_L = 0.53\)).

Manufacturers of butterfly valves

Buracco : www.buracco.com
Robvalve : https://robvalve.wixsite.com/
ABZ Valves
Keystone Butterfly Valves (Emerson)
Nibco Butterfly Valves

4. Gate valves

What is a gate valve ?

Gate valves are intended strictly for fully open (isolation) or fully closed on/off service. They should not be used as throttling control valves because fluid velocity at partial opening generates severe disc fluttering, gate seat scouring, and chattering vibration.

Manufacturers of gate valves

UCMA valves : www.ucmasn.fr
PAM valves : https://www.pamline.fr

5. Ball valves

What is a ball valve ?

In a ball valve, the closing element is a sphere with a central flow bore. Rotating the ball by \(90^\circ\) opens or closes the flow path. Segmented ball valves featuring a notched V-contour (V-notch or V-ball) provide an equal percentage characteristic and high shearing capability for fibrous pulps, slurries, and viscous media.

Flow parameters of ball valves (V-Notch)

The values below are given by Emerson Fisher for typical rotary V-notch control ball valves:

Valve size (NPS)	Degree of opening	Cv	F_L	X_T	F_D
1	60	15.6	0.86	0.53	-
1	90	34	0.86	0.42	-
1-1/2	60	28.5	0.85	0.5	-
1-1/2	90	77.3	0.74	0.27	-
2	60	59.2	0.81	0.53	-
2	90	132	0.77	0.41	-
3	60	120	0.8	0.5	0.92
3	90	321	0.74	0.3	0.99
4	60	195	0.8	0.52	0.92
4	90	596	0.62	0.22	0.99
6	60	340	0.8	0.52	0.91
6	90	1100	0.58	0.2	0.99
8	60	518	0.82	0.54	0.91
8	90	1820	0.54	0.18	0.99
10	60	1000	0.8	0.47	0.91
10	90	3000	0.56	0.19	0.99
12	60	1530	0.78	0.49	0.92
12	90	3980	0.63	0.25	0.99
16	60	2380	0.8	0.45	0.92
16	90	8270	0.37	0.13	1.0

Manufacturers of ball valves

Guichon valves : http://guichon-vannes.com/
GRK valves : https://www.grk.fr/

Source References

[Aimonen] Globe valve engineering drawing, Wikipedia Creative Commons
[Padleckas] Globe valve cross-section diagram, Wikimedia Commons
[Emerson] Control Valve Handbook, 5th Edition, Emerson Fisher Controls International LLC
[Midoux] Mécanique et Rhéologie des Fluides en Génie des Procédés, page 392, N. Midoux, Lavoisier Tec & Doc