# Fluid dymanics basics ball valve full open vs. half open

• Mick McCormick
In summary, the conversation discusses the potential differences in using a ball valve with 100 psi jet fuel on one side and atmosphere on the other, depending on the pressure and degree to which the valve is open. The speaker notes that there may be a significant difference due to the restrictive points and turbulence caused by a half-open valve, which may only allow for 30% of the full flow area. The speaker also mentions an Excel calculation that shows at half-open (45°), the flow area on each end is only 39% of a full bore valve. Additionally, there may be extreme turbulence to consider.

#### Mick McCormick

is there any difference and why ? I have a ball valve with 100 psi jet fuel on one side and atmosphere on the other end ? Is there any difference if o have 100 psi and the valve all the way open vs. say 200 psi and only half way open . Please explain ?

I think there will be a significant difference... for starters, a half-open ball valve has 2 restrictive points (each side of the ball), and depending on the ratio of the size of the ball compared to the size of the hole through it, half-open may only be 30% of the area... This will also introduce a LOT of turbulence

I just realized I still have an old Excel calculation I developed to determine to of flow area vs ball valve opening angle; and, taking a quick look at he graph curve of that calculation shows that at 1/2 (45°) open the flow area on each ball end is 39% of the full open area of a full bore ball valve. In addition, there will also be the extreme turbulence issue stated by Rx7man.

Rx7man

## 1. What is a ball valve and how does it work?

A ball valve is a type of valve that uses a spherical ball with a hole in the middle to control the flow of fluid. When the valve is in the open position, the ball is turned parallel to the direction of flow, allowing the fluid to pass through. When the valve is in the closed position, the ball is turned perpendicular to the direction of flow, blocking the flow of fluid.

## 2. What is the difference between a full open and a half open ball valve?

A full open ball valve allows the fluid to flow freely through the valve, with minimal resistance and pressure drop. A half open ball valve, on the other hand, only allows partial flow through the valve, resulting in higher resistance and pressure drop.

## 3. When should I use a full open ball valve versus a half open ball valve?

A full open ball valve is typically used when maximum flow rate is desired, and pressure drop is not a concern. A half open ball valve is often used when flow rate needs to be controlled or reduced, or when pressure drop needs to be minimized.

## 4. Can a ball valve be adjusted to any position between full open and half open?

No, a ball valve can only be fully open or fully closed. Attempting to adjust the valve to an intermediate position can cause damage to the valve and result in leakage.

## 5. Are there any other factors to consider when choosing between a full open and half open ball valve?

Yes, other factors to consider include the type of fluid being controlled, the pressure and temperature of the fluid, and the overall system requirements. It is important to consult with a professional to determine the best type of ball valve for your specific application.