Ball Valve How it Works

What is a Ball Valve ?

A ball valve is a rotational motion (quarter turn),quick rotating valve that uses a ball-shaped disk to stop or start or regulate fluid flow.The function of this type of valves,ball is same as of disk in globe valve. When the valve handle is turned to open the valve, the spherical ball rotates to a position where the hole through the ball is in-line with the valve body inlet and outlet of flow. When the valve is shut, the ball is rotated so  that the hole is perpendicular to the flow openings of the valve body and the flow is stopped. 

Ball valve actuators are of the quick-acting type, which require a 90° turn of the valve handle to operate the valve. Some ball valve actuators such as planetary gear-operated,  allow the use of a relatively small operating force to operate a fairly large valve.

Some ball type valves have been developed with a spherical surface coated plug that is off to one side in the open position and rotates into the flow passage until disk blocks the flow path completely. 

Advantages of Ball Valves

• A ball valve is the least expensive of any valve arrangement
• Ball valve offers low maintenance costs.
• Ball valves are compact, require no lubrication, and give tight sealing with low torque.

Disadvantages of Ball Valves

• Ball type valves(especially old designs) have relatively poor throttling characteristics.
• In a throttling position, the partially exposed seat of ball valve rapidly erodes because of the impingement of high velocity flow.

Ball valve

Valve Materials in Ball valves

Balls are usually metallic with trim (seats) produced from elastomeric (like rubber) materials. Plastic construction in ball valves is also available.

The resilient seats for ball valves are made from teflon (TFE), filled TFE, Nylon, Buna-N, Neoprene, other combinations of these materials.Because of these elastomeric materials ball valves cannot be traditionally used at elevated temperature and engineer must take care while selecting ball valve for particular application.

Ball Valve Port Patterns ,Bonnet & Stem Design

Ball valves are available in the venturi, reduced, and full port pattern. The full port

pattern has a ball with a bore equal to the inside diameter of the pipe.

The stem and ball connection is explained here.The stem in a ball valve is not fastened to the ball. It normally has a rectangular portion at the ball end which fits into a slot cut into the ball. The enlargement permits rotation of the ball as the stem is turned. A bonnet cap fastens to the body, which holds the stem assembly and ball in place. Adjustment of the bonnet cap permits compression of the packing, which supplies the stem seal. Packing for ball valve stems is usually in the configuration of die-formed packing rings normally of TFE, TFE-filled, or TFE-impregnated material. Some ball valve stems are sealed by means of O-rings rather than packing.

Ball Valve Positions

Some ball valves are equipped with stops that permit only 90° rotation. Others do not have stops and may be rotated 360°. Whether there is stop available or not, a 90° rotation is all that is required for closing or opening a ball valve.

The handle indicates valve ball position. When the handle lies along the axis of the valve, the valve is open. When the handle lies 90° across the axis of the valve, the valve is closed. Some ball valve stems have a groove cut in the top face of the stem that shows the flowpath through the ball. Observation of the groove position indicates the position of the port through the ball. This feature is particularly advantageous on multiport ball valves.

HVAC Applications of Valves

HVAC Valves are such components without which we cannot control flow in pipes .Valves are needed for every media whether it is water, gas, air or any other liquid. Valves would have been needed for solids if they could have ability to flow. Like other areas, valves find its extensive use in HVAC (heating, ventilation and air-conditioning).

With special focus on HVAC, following are the some major hvac application of valves.

• Water Chiller, the heart of HVAC system, has valves on inlet and outlet lines of chilled water and cooling water. These valves are usually gate and globe valves which are used for isolation and throttling purposes. Water chiller operates on vapor compression cycle or vapor absorption cycles which also require valves internally as a requirement of thermodynamics. For example Refrigerant expansion valve is needed inside a water chiller cycle. Chilled and cooling water headers also need valves for isolation and heating/cooling changeover.
• Similar to water chillers, HVAC hot water generator has also valves on its inlet and outlet for isolation and flow control purposes. If water chiller can also act as water heater then there is no need of hot water generator obviously.
• Chilled water pumps and cooling water pumps have also isolation and throttling valves on their inlets and outlets. When we talk about water pumps then there are also check valves at the outlet of pumps to prevent reverse flow.
• Cooling towers are another hvac equipments which require valves at inlet and outlet for flow control of cooling water. Sometimes a float valve is also in the basin of cooling tower to control the level of water in cooling streams. Valves would also be needed for make-up water lines in HVAC system and cooling towers.
• Air handling units (AHUs) also need valves at inlet and outlet to regulate chilled water as per demand of cooling in the spaces depending upon the type of HVAC control system. These air handling unit valves are also connected to some HVAC software to remotely operate them as per cooling/heating demand from HVAC users. Drain valves are also provisioned inside air handling units.
• If Fan Coil Units (FCUs) are installed in individual rooms then valves will also be installed at entry and exit of these units to have precise control of cooling /heating for occupants of that space.