# What is equal percentage?, what is linearity in PICV? What is valve stem? What is stroke time? What is hold off pressure, close off pressure?

## Equal Percentage:

• Control valves and pressure-independent control valves (PICVs) typically utilize the term “equal percentage” to express the link between valve plug movement and flow rate.
• In an equal percentage characteristic, equal increments of valve plug travel produce equal percentage variations in flow rate.
• This nonlinear connection enables precision flow control over a wide range of valve positions, making it very valuable in applications that require precise control.

## Linearity in PICV:

• Linearity in Pressure-Independent Control Valves (PICVs) describes the proportional relationship between the control signal and the actual flow through the valve.
• A linear PICV’s flow rate changes linearly with the control signal, resulting in a predictable and consistent response.
• This linearity is critical for accurate and reliable control in HVAC (Heating, Ventilation, and Air Conditioning) systems, since it ensures that the intended flow is achieved in response to changes in control input.

## Valve Stem:

• The valve stem is an essential part of a control valve. It is a rod that connects the actuator (the valve’s moving mechanism) to the valve plug or disc.
• When the actuator receives a signal, it moves the valve stem, which causes the valve to open or close.
• The valve stem’s design and construction are critical for ensuring consistent and precise fluid flow management in a variety of industrial processes.

## Stroke Time:

• Stroke time refers to how long it takes for a control valve to transition from fully closed to fully open.
• It is an important parameter in control systems because the speed and precision of the valve response affects the overall performance of the control loop.
• Short stroke periods are desirable for quick and efficient control, particularly in operations that demand rapid flow rate modifications.

## Hold Off Pressure and Close Off Pressure:

Hold off pressure and close off pressure are terms associated with control valves and their sealing capabilities.

### Hold Off Pressure

• This is the minimal differential pressure required to keep a control valve closed.
• Hold off pressure keeps the valve from unintentionally opening due to low differential pressure, ensuring stability in the closed position.

### Close Off Pressure:

• The maximum pressure at which a control valve can block off the flow when fully closed. It measures the valve’s ability to totally shut off the fluid without leaking.
• Understanding close-off pressure is critical when selecting the proper valve for applications that require a tight shut-off.
• The equal percentage, linearity, valve stem, stroke time, hold off pressure, and close off pressure are important terminology in the field of control valves and pressure-independent control valves.
• Each term is critical to providing the effective and precise management of fluid flow in industrial operations, notably in HVAC systems and other applications where accurate control is required.