Tuesday, October 9, 2012

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 animation

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 pictures
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.

Friday, October 5, 2012

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.

Thursday, October 4, 2012

Tips for HVAC System Engineers

As HVAC system engineer, one has to keep an eye on all factors and areas that can decrease the efficiency of system or increase downtime or HVAC system unavailability or increase the maintenance cost of heating, ventilation and air-conditioning system. The responsibility starts from very beginning, when you decide to install HVAC system and start working on it in any way.

Following are the tips for smooth, trouble free and economical operation/working of hvac system.

  1. Start your working from the very early stages of hvac system selection, procurement and tendering. Don’t ignore all these pre-installation steps as it would become difficult at later stages to alter any pre-done work. Complete your home work in selection of type of chillers you are going to install for your building or space or for other purposes. Consult hvac experts for getting pros and cons of different types of chillers and select the one which suits your resources and priorities. Then select the renowned and reliable manufacturer for purchasing the hvac system components. Get involved in tenders to ensure transparency in whole process.
  2. HVAC Installation is very important phase for hvac engineers. Include all essential items and accessories in hvac contract BOQ and monitor the activities of hvac contactor so that all goes in accordance with boq or terms and conditions written while awarding contract. Ensure that all installation is carried out in accordance with drawings and all components meet the specifications mentioned in BOQ. Your saving at any stage could lead you to spend more in later stages. Never compromise the material of all items being installed in hvac system. Low quality material would finally take you to problems in coming days/years. Commissioning is as important as its installation so adhere to commissioning procedures at all times and don’t ignore any thing in courtesy.
  3. Training of hvac personnel is very important in operation and maintenance point of view. So include training of your personnel in contract or arrange it separately. Your expenditure on manpower training would pay back you in future so never overlook it.
  4. Prepare all hvac procedures related to operation and maintenance of each and every component of hvac system and implement it strictly. Adhere to maintenance program for your water chillers, air handling units, cooling towers and fan coil units .Your adherence to maintenance programs would never let you face any problem regarding the unavailability of hvac system. Always try to complete maintenance work timely in the best available resources or with the support of hvac supplier
  5. Adopt hvac pro-active approach regarding critical and heat transfer interfaces/surfaces or to operate hvac system at maximum efficiency, focus on heat transfer interfaces/surfaces. In this regard condenser is most important, keep it at optimum conditions. Scaling, corrosion and high pressure in condenser would get you in trouble finally so be pro-active before your condenser lets you down. Heating and cooling coils are also equally important as these would directly affect cooling or heating in hvac spaces/zones. Get all coils cleaned and keep them in best heat transfer condition. Ensure timely maintenance of cooling towers to operate them at maximum efficiency/effectiveness.

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