Copper flow controller
A control valve is used to control a current by resizing the current flow, which is driven by a signal from a controller, such as a on-screen PID controller in a flowmeter. This is one of the most widely used accessories in flow control.
Accessories for copper flow controller
Control valves can be used as a combination of mass flow controllers and pressure controllers or as a separate component in combination with a flowmeter or pressure gauge. Together with a feedback loop from the mass flow controller or pressure controller, the valve controls the amount of current flowing through it to impose a pressure or pressure flow point.
Depending on the application, it is often unclear whether your copper flow controller requires a valve (open-closed) or a control valve, or whether a valve is normally open or normally closed. In the group of control valves, there are a number of different valves, each of which has its own parameter range, advantages and disadvantages.
In this blog, I will highlight some of the valves and how to cope with higher absolute and differential pressures and how to achieve higher pressures at lower differential pressures.
The direct control valve consists of a flow control valve and a controlled surface that determines the size of the opening through which it can pass and thus determines the amount of flow through the valve.
- Advantage: Such a valve is relatively fast, inexpensive and uses little energy to control the flow.
- The downside is that it can only withstand limited pressures and currents.
Let’s use a solenoid valve as an example:
For the valve, the force (F) required to overcome the opening of the valve is determined by the size of the diaphragm diameter (d) and the pressure difference (Δp) on the valve (F ~ Δp * ¼ d2).
The solenoid valve can only apply a force of about 5 N. This could be a possibility of using a stronger coil and a larger magnetic force. However, mass flow controllers often have a limited power supply and the amount of heat generated can become a problem. The result with maximum maximum flow is proportional to pressure and diameter.
In short, most direct control valves are not suitable for high flow, or for applying high differential pressures or absolute pressures due to these limitations. Direct control valves can be used for a flow of less than 1 ml per minute to approximately 50 liters per minute.
What options do we have?
- Reset the direct valve for higher pressures
- Indirect control valve using 2-phase valve
- Use the pressure relief valve to achieve high flow at low pressures
1- High pressure control valve
The easiest solution to deal with higher pressures is to redesign the direct control valve. Because the nozzle size is limited, it can be used for relatively small flows (up to 20 liters per minute). To handle the larger pressure difference, up to 200 bar differential pressure (bar), valve and mass flow control body must be stronger. Most valves cannot support 200 bar. Either the sealing material can rupture, or the mechanical parts will not be able to withstand sudden pressures of force at 200 bar.
The dimensions of the valve are only smaller than a normal valve and hence the whole mass controller. On the other hand, low currents are often limited due to leakage through the valve at high pressure differences.
2. Indirect control valve (two-phase control valve)
To move to higher pressures, we need to take a bigger step in changing our mass flow control. With a so-called indirect control valve (Figure 1), higher currents, absolute pressure and higher differential can be achieved.
Indirect control valve (or two-phase control valve) includes the following:
- Pilot direct valve (A) controlled, with the behavior previously described, and without the need for additional force.
- Excess milk in the body; A pressure compensation section (B) to maintain a constant pressure difference (P1-P2) only
Several bars in the pilot valve (A). By doing this, both the inlet and outlet pressures may be changed without affecting the performance of the valve. The pressure force more than the pressure compensation part keeps the valve closed. Only when the upper valve is opened does the pressure gauge open slightly to open the valve and control the flow.
Therefore, the indirect control valve consists of two valves in series (A + B), which determine both the pressure drop and the size of the holes next to each other.
The disadvantage of this valve is its size and relatively high costs. In addition, a smaller pressure difference is required to close the valve pressure relief section. Also, the cavities are still limited in size, so a minimum inlet pressure> 150 bar is required to reach 200 liters per minute. To obtain such flows at low pressures, a completely different type of valve, such as a pressure relief valve, a lower valve is required.
3. Pressure relief valve
Larger valves can be used to reach higher flows with a direct control valve, but this must reduce the pressure in the valve. This can be done with a pressure relief valve, in which the effective pressure hole can be significantly reduced (Figure 2). With a lower valve, flows of several hundred liters per minute can be achieved with a minimum pressure difference. However, the absolute pressure is limited due to the design and the valve is much larger and more expensive than a conventional direct control valve.
Depending on the pressure you want to have your mass flow controller and the output current you need, you can use it:
- High pressure controlled direct valve (maximum 200 bar and 20 liters per minute), or
- Indirect pressure relief valve (maximum 700 bar or 400 bar and 200 liters per minute).
To achieve high flow at low pressures, a pressure relief valve will be the best solution.
Take a look at the control valves we often use in combination with our flow meters or pressure gauges.
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