My answer was that standard with the VFD pump combination instead of a valve had these advantages:

1. Dramatic reduction in energy costs by eliminating the pressure drop is achieved through the pump;
2. Greater control by eliminating the control valve hysteresis or stickiness;
3. Faster and more responsive flow control valve by eliminating the mechanical action;
4. Elimination of a source of fugitive emissions;
5. Electricity savings from improved power factor of the system.

I have not yet succeeded, these benefits of the VFD anyone actually used this way confirmed.
Barriers

The participants in my survey said the main obstacles to the use of VFD pumps are these:

1. Tradition. “We always use a control valve;
2. The VFD is purchased by a purchaser buys other than the person, the control valves;
3. VFD have a history of unreliable;
4. Our pumps are not designed for use with variable speeds and would be non-linear control use;
5. We have never considered an alternative to a control valve.

The analysis of the benefits

If the energy savings were small, this would be a moot point. However, there are many processes that pumps liquid into the pump to a high head, only to lose that energy, if it appears the pressure drop across a valve, that this source of energy loss up to 25% of that energy to a refinery, chemical or paper mill operation. Even if we designed our processes from the outset with the VFD pumps, we have much smaller electric motors.

There are two factors at work. We know that the flow speed with centrifugal pump speed linear physical laws, which is directly attributable to the perception of non-linearity of paragraph 4. We also know that the electrical current is needed to produce the pump at lower speeds on the main street less than required drive is proportional to the cube of speed ratio. So, by the valve is completely out of the flow path of the amount of stored energy is much larger than one would expect. Of course, less load on the electric motor also means a longer life.

One of the features of the VFD pump combination is the speed of the reaction. Otherwise change the time as the valve in the pressure drop repositioning must stick to the electric motor of the pump to respond within a few cycles of the new spectrum to the new synchronous speed reference work. can react, the speed of the VFD pump to the new current set value so fast that the speed setpoint is ramped necessary to prevent the hammer effect can occur in the process with fluid-filled system when the speed increases.

It is known that the mentioned problem introduced in the tuning of the PID control loops, the variable in the flow loop through the control valve stickiness hysteresis. The valve also leads to a delay caused by mechanical movement of the valve engine. Loops that should be optimized at the factory start-up phase displeased if, the stickiness of the building control valve or the loop to become unstable. In fact, incorporate the latest process control loop auto-tuning software, the actual valve hysteresis compensation up to a point. The loop is detuned gradually, continuing to establish the cause for the process set values ​​for the increased variability due to process upset the flow and pressure control. Today we seem to be that kind of sub-optimal process performance to accept, but we can do better by taking the main source of the error-control valve with a VFD / pump.

The gain from the abolition of the famous fugitive emissions from the packaging of the control valve is clear, if the valve is removed. A less obvious advantage of using a VFD instead of discrete motor starters and electrical switches, operating at a near-linear performance factor. The VFD presents the network as a resistive load with a power factor. When an AC induction motor is placed over the power line, as in a conventional valve position, usually the induction motor is to the power supply with a power factor that can of about 0.7 to 0.9 range range, depending on load and ratings for the engine. This performance means that the amount of electricity consumed by the plant directly to any AC induction motor, the measured power was divided by power connected. In many systems with many of these directly connected three-phase induction motors, which require electric utilities to the use of parasitic capacitances in each phase of the AC cable placed only for the reactive power compensation. Parasitic capacity is required large investments and a constant load on the electrical power plant. Use of VFD eliminates the need for parasitic capacitances because they self-correct for power factor within their own circuits.

   Have you checked the car for your tutorial system at one point or another?

   Have you ever had an industrial air hammer?

   Have you ever installed an electric bell?

     If the answer to any of these questions, then you are probably know what a solenoid valve.

hydraulic solinoid valve

Solenoid valves are electromechanical valves, by stopping or movement of electricity through a coil to be controlled to change the status of the valve. A coil is a coil of wire, the magnetic when electricity runs through them.

     Solenoid valve to activate when using this coil, the valve, thereby controlling water flow, airflow and other things with electricity.

    In general, there are three types of solenoid valves: The all-purpose type, a type of low-pressure steam and high pressure steam type.

   Solenoid valves are composed of several parts, such as wrapping, covering electrical connector nut, cartridge seal, O-ring connector end, body and nut.

  All these components are critical to the overall performance of the solenoid valves. If a malfunction, it will affect the overall operation of the automotive system for beginners as well as industrial air hammer and installation of electric bell.

   Therefore one must always be maintained and regularly inspected to

Valve Coil

 maintain the solenoid valves work best. But like all other parts of the starter system, an air hammer and an electric bell, the solenoid valve can be damaged after a certain time. Thus, solenoid valve replacement will be necessary. It? Good thing is that many dealers, the quality solenoid valves and inexpensive service. Forget when selecting valve coil, not you, check the valve type, mesh size, pressure rating, coil voltage and the type of connection to each port. Gates provides detailed information on valves, EGR valves, solenoid valves, ball valves, etc.. Valves in conjunction with copper sinks.

An altitude valve controls the level of a reservoir. The altitude valve will remain open while the tank is not full and will be closed when the reservoir reaches its maximum level. The opening and closing the valve requires no external power source (electric, pneumatic or power of man), it was done automatically, hence its name.
Control Valves
A control valve regulates the flow or fluid pressure. Control valves normally respond to signals generated by independent devices such as flow meters or temperature gauges. The control valves are normally fitted with actuators and positioners. Globe valves are widely used tire for control in many sectors, although quarter-turn types such as (amended), ball and butterfly valves are also used.
Regulation of the valves can also work with hydraulic actuators (also known as hydraulic pilots). These types of valves are also known as Automatic Control Valves. Hydraulic actuators in response to changes in pressure or flow, and open / close the valve. Valves automatiche di controllo non richiedono Sorgente di una alimentazione esterna, il che significa che la pressione del fluido è sufficiente per aprire e chiudere the valvola. Automatic control valves include: pressure reducers, valves, flow control, back support pressure valve, altitude valves and safety valves. An altitude valve controls the level of a reservoir. The altitude valve will remain open while the tank is not full and will be closed when the reservoir reaches its maximum level. The opening and closing the valve requires no external power source (electric, pneumatic or power of man), it was done automatically, hence its name.