Gate Valve Parametric Study

Gate Valve :

• Gate valves are widely used for all types of applications and are suitable for both above-ground and underground installation. Not least for underground installations it is paramount to choose the right type of valve to avoid high replacement costs.
• Gate valves are designed for fully open or fully closed service. They are installed in pipelines as isolating valves, and should not be used as control or regulating valves.
• Operation of a gate valve is performed doing an either clockwise to close (CTC) or clockwise to open (CTO) rotating motion of the stem. When operating the valve stem, the gate moves up- or downwards on the threaded part of the stem.
• Gate valves are often used when minimum pressure loss and a free bore is needed. When fully open, a typical gate valve has no obstruction in the flow path resulting in a very low pressure loss, and this design makes it possible to use a pipe-cleaning pig.
• A gate valve is a multiturn valve meaning that the operation of the valve is done by means of a threaded stem. As the valve has to turn multiple times to go from open to closed position, the slow operation also prevents water hammer effects.

Geometry used for simulation :

• We use a basic geometry of the gate valve which consists of different components like gate disc, Bottom , Spindle, Spindle wheel & Bonnet.
• Here we can move the gate disc up or down to our desired value to simulate the flow.
• We are going to handle the simulation with only the fluid volume as we are interested only on the flow of the fluid.
• Thus from the geometry we will extract the fluid volume.

Solid Geometry : Fluid Volume edges :

• By extracting the volume around the 3 highlighted edges we can get our fluid volume.
• For better visualisation we can pull the inlet & outlet edges further as shown in the figure below.

• The gate disc can be moved to increase or decrease the opening of the valve.
• A cut plane can be useful to visualise the opening of the valve.

Small Opening :

Large Opening :

Computational Meshing :

As we have a larger fluid volume we can satisfy our results on the baseline mesh which gives sufficient amount of elements even between the small gaps between the openings of the valve.

Setup & Simulation :

• The setup for all the openings are the same.
• We give a value for gravity for more accurate results.
• Set the fluid material as water. Change the fluid material in the cell zones.
• The steady state simulation can be initialised using standard initialization.
• The inlet boundary condition is set to pressure inlet for a gauge pressure of 10 pascals.
• Now we can give the plots required and calculate the simulation.
• As we are analysing results for varying length of the opening, we can parametrice the input & output values. transfer the parametric values to Excel for further calculations.

• This clearly shows us that the increase in the opening increases the flow rate of the valve.
• A graphical representation will show the obvious growth of flow rate.

• We can further find the differences through the velocity contours.
• As the opening is increasing the resistance to the flow decreases, which results in the increase in the velocity of the flow of water.

10% Opening :

20% Opening :

30% Opening :

40% Opening :

50% Opening :

60% Opening :

70% Opening :

80% Opening :

• These images shows us the flow of the water inside the valve pipe.
• We can see that as the opening is enlarged the flow velocity of the water is increased.

Flow Coefficient & Flow Factor :

• Valve Flow Coefficient (Cv) is a valve’s capacity for a liquid or gas to flow through it. It is technically defined as “the volume of water at 60°F (in US gallons) that will flow through a valve per minute with a pressure drop of 1 psi across the valve.”
• In simpler terms, the larger the opening in a valve, the larger the Cv. As a valve is opening, the Cv increases until the valve is fully open, where it reaches its highest possible Cv, or 100% open Cv.
• 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 called as Flow Factor.
• Cv = Q * √ (SG/ ΔP) (units in US GPM, psi) ΔP = Differential Pressure (psi) Flow factor (Kv) is the metric equivalent of flow coefficient and is defined as: the flow of water in meters cubed per hour (m³/hr) at a pressure drop of bar.

where:

Q is the rate of flow (expressed in US gallons per minute),SG is the specific Gravity of the fluid (for water = 1),ΔP is the pressure drop across the valve (expressed in psi).

The metric equivalent flow factor (K_v; commonly used in Europe and Asia) is calculated using metric units :

where

K_v is the flow factor (expressed in ).

Q is the flowrate (expressed in cubic metres per hour []),

SG is the specific gravity of the fluid (for water = 1),

∆P is the differential pressure across the device (expressed in [bar]).

K_v can be calculated from C_v using the equation:



Conclusion :

The mass flow rate at the outlet of the valve can be controlled by controlling the amount of opening inside the valve.

The calculations for the flow rate & valve opening can be taken easily through parametric solving.

The larger the opening in a valve, the larger the Cv. As a valve is opening, the Cv increases until the valve is fully open.

Thus we can conclude that the flow rate calculations can be done accurately using this simulation.