A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction.
Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, and inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.
The simplest possible check valve consists of a ball that is free to move over a limited displacement. In one extreme position, it is fully closed and completely blocks the flow, and in the other extreme position, it is fully open. In equilibrium, the position depends on the pressures at the two hydraulic ports.
Let us have a look at the simplest way to model a check valve using the Hydraulic library. Most of you might be familiar with the CV010 component as shown below. It is a functional model of a hydraulic check valve with a linear characteristic. The valve is normally closed. When the pressure drop across the valve exceeds the check valve cracking pressure (typically a spring force), the valve opens and let the fluid flow across so that the pressure drop gets regulated to the cracking pressure. Pressure at ports 1 and 2 are input variables. The flow rate is computed and output at both ports. The flow rate / pressure drop characteristic is linear during the valve regulation. A functional hysteresis can be specified to the model in order to take into account dry friction effects.
CV010 is used as a first step in modeling a functional check valve. CV012 is used when the valve saturation should be considered (valve completely open). Detailed check valves can be modeled using the Hydraulic Component Design library. You can find these in the Simcenter Amesim documentation but let us look further into the parameter settings and what we are trying to achieve through this article.
The main parameters in this particular submodel are as shown below:
As you can see above, the Flow rate to pressure drop characteristic is linear and as mentioned above, you can use Hydraulic component design library to model the complex characteristics. But that is not the objective of the article, we are trying to investigate how we can model a one-way flow with non-linear pressure drop characteristics using the HR2P00 component. Let us look at HR2P00 component and further details on that.
HR2P00 is a submodel of an orifice with non symmetrical pressure drop characteristics defined by the user. A pressure in [bar] is an input at each port and a flow rate in [L/min] is computed to be an output at both these ports. This submodel uses pressure drop characteristics defined in 1D or 2D data file. The pressure drop characteristics are defined by 2 different data files :
- - the 1st : when the flow direction is from port 1 to port 2.
- - the 2nd : when the flow direction is from port 2 to port 1.
And the main parameters for the component are as follows:
Here the Pressure drop characteristics can be defined via 4 methods:
- Pressure loss coefficient (ζ) is set as a function of Reynolds number : ζ = f (Re)
- Flow coefficient (Cq) is set as a function of Reynolds number: Cq = f (Re)
- Pressure drop coefficient (zeta) is set as a function of flow number (lambda): ζ = f (λ)
- Flow coefficient (Cq) is set as a function of flow number (lambda): Cq = f (λ)
You can use any method to define it but for this example we will use Flow coefficient as a function of flow number to define our one-way flow.
One way to do this is to input a table for flow direction 2->1 as follows:
If you follow this approach, Simcenter Amesim will complain that there are zero Cq values and this is unacceptable. One way to get around this to define a very small value for Cq for example 10e-4 instead of zeros.
Another typical problem which the engineers would encounter would be having Cq vs lambda as a function of temperature (T) from CFD correlations. Currently a workaround available to incorporate this would be to use the Submodel editor as follows:
Open Submodel Editor by going to Tools -> Submodel Editor:
Open the HR2P00 submodel and add an input port. Define all the necessary definitions for the port i.e. the input type, Unit and also the input/output as shown below:
As you can see above, we are trying to use y0 which is nothing but the geometric restriction variable present in the parameters. The idea behind this is to use the geometric parameter which is unchanged for this type of analysis to be varied as a temperature input which can be supplied by the user as a M1D table
Delete the original y0 from the Real Integer parameter list. Pick an appropriate image for your submodel and save it in a category.
So there you have it, you can use the new submodel which can calculate the pressure drop for different temperatures and also could be used as a one-way restriction with the table adjustments mentioned above.