When Blackhawk supply control valves, company is defining this type of valves, it is imperative:
- To correctly identify the different scenarios where the valve should work.
- Establish between which ranges the valve will work to control the process in each of the previous scenarios.
- It is widespread for engineers to mix these two concepts. One thing is to analyze the different scenarios of the process, and another thing is to analyze the ranges with which the valve will regulate each scenario.
- Identify the possible scenarios, as its name indicates, is to identify the possible situations in which the process can be found. This could mean different pressure conditions, temperatures, flow, such as the start-up of an industrial plant, the shutdown or the situation of full load, etc.
On the other hand, the ranges required in each scenario are the possible variations, mainly inflow and pressure that may arise in each scenario.
Example:
Two pumps send water to a tank, and in the middle, controlling the flow, we have a regulation control valve.
I&C Control Valves
A process engineer has decided that two scenarios be studied in the process:
1st- That one pump is working
2nd- Those two pumps are working.
Scenario 1 (A Pump Running)
Control Valve Scenarios
In this first scenario, the process engineer must indicate the process variables’ ranges, where the valve has to work when there is a pump running.
To specify this range, maximum, average, and minimum values are usually established.
Stage 1 data (Operating range with one pump running)
Control Valves Data
With these data, it is being indicated that with one pump running, Blackhawk supply control valve almost entirely opens should give a range greater than 10kg / s, which will typically work around 8.7Kg / s, and that it has to be able to regulate a minimum flow of 1kg / s. s.
Control Valve Turndown
Scenario 2 (2 Pumps Running)
Processes With Control Valves
In this case 2, the process engineer must again indicate the ranges of the process variables where the valve has to work.
Control Valves Inputs
There are three typical errors when process engineers specify process data.
By performing fewer calculations instead of studying the valve’s behavior in each scenario, it is proposed to study a minimum, average, and maximum of a mixed scenario of all. Doing this makes it impossible to adequately evaluate how the valve acts under the different circumstances of the process.
Be careful, and this is not intended to say that you always have to analyze all the possible scenarios of the process and all the possible ranges. It simply points out that, in many cases, it is not worth just analyzing three points (minimum, average, and maximum), such as usually required in the customer’s specifications, experience, and common sense will show engineers which scenarios deserve to be studied.
The second most common error in the process data is that the processor could require too wide operating ranges in each situation. In the previous example, there was a minimum of 1kg / s and a maximum of 27kg / s. This implies a turndown of 27/1, which in many cases could be an excessive requirement. To oversize the equipment or damage it, it is convenient to limit the turndown as much as the process allows, or in other words, sometimes you have to ask the process engineer why the valve is required to control that operating range is?
Another widespread error in the process data is that “the pressure drop defined in the valve is not the most adequate.” This point will be tried to explain later.
There is a typical error when instrumentation and control engineers specify a modulating control valve. Trying to specify the valve, based solely on the process data: “not enough”.
To be able to correctly specify a regulation control valve, not only data is needed, it is necessary to understand the function of the valve within the industrial process, and this in most cases, usually requires getting up from the chair and “SITTING WITH IT. PROCESS ENGINEER “to clarify all concerns.
Defining the process data of an On-Nothing valve is widespread in this type of valve to give excessive importance to the process data.
In most cases, to correctly specify this equipment, it is necessary to focus mainly on three aspects:
- The design conditions (pressure and temperature)
- Maximum shutoff pressure (maximum process pressure that the actuator will have to overcome)
- Minimum times required for closing and opening of the valve.