Vent Management on Large Cavity Steam Heat Exchange Equipment Commonly Found in the Brewing Industries: Thermostatic Air Vents (TAV) and Vacuum Breakers (VB)

The following represents a primer on vent management devices on steam heat exchange equipment: TAVs, VBs, and the combination device, model TAVB-3. In order to do that, we will review the purpose and proper application of the devices to establish clarity.

What are Vacuum Breakers and why do we need them?

Vacuum breakers are spring-loaded valve and seat devices that are mounted on or near the steam space of a heat exchanger allowing steam pressurization of the space, but during throttling down or shut off of steam supply also allow the valve to overcome the spring force and open when vacuum is present. The vacuum is formed when steam, with its much higher specific volume than water, condenses to water with heat exchange and is not replaced in the heat exchange space with an equivalent volume of steam, i.e. when the control valve is throttling down from its process design maximum flow, or when steam is being shut off after completion of the process step. By “breaking” the sub-atmospheric condition which occurs in those situations by allowing air into what was the steam space through the open vacuum breaker device; condensate drainage from the heat exchanger by gravity is enabled. This prevents water hammer, internal corrosion, gasket or joint leakage, and potential damage to the heat exchanger and other equipment. Without this device, a reverse pressure differential is formed in the steam space due to vacuum which will suck available condensate from the return system into the calandria, coil, or other large cavity heat exchanger.

Stainless Steel Thermostatic
Air Vent/Vacuum
Breaker (TAVB)

What are Thermostatic Air Vents and why do we need them?

Thermostatic air vents (TAV) are also valve and seat devices that are actuated by temperature, typically a “balanced” bellows. The bellows has an alcohol and water charge inside that evaporates and expands on temperature increase approaching the steam saturation curve for the particular steam pressure. The expanding bellows drives the valve into the seat and closes the device. On steam start-up of the heat exchanger, cool air is expelled quickly by using this device until steam reaches it which quickly closes the valve. Similarly, on decreasing temperature, at some point a few degrees lower than the steam saturation curve, the mixture in the bellows condenses and contracts the bellows which pulls the valve plug away from the seat and thus opens the vent. This signifies that non-condensable gases have accumulated and the temperature has depressed enough to allow the valve to open and expel them from the steam space. Pressure is inconsequential up to the TAV design pressure since the alcohol charge is designed to follow the steam saturation curve, offset but parallel, always activating a few degrees below saturation temperature for any given pressure (including vacuum).

Doesn’t the Steam Trap do this as one of its functions?

It is true that one of the three primary functions of the steam trap is to remove non-condensable gases. By virtue of the modularization of steam supply and condensate removal equipment at some distance away from the internal heat exchangers of kettles and cookers for example due to floor space restrictions in the brew house, size, configuration, and internal area of heat transfer equipment in modern breweries and the demands of production, it is imperative that these supplemental devices be used to remove these gases as close and as quickly as possible to the area where they would be entrapped: opposite the steam supply connection of the exchanger.

Why is it so important that air be removed?

There are several reasons, but most importantly, air is an excellent insulator and, without removal, serves to insulate internal heat transfer surfaces from the steam trying to transfer its latent heat. Surface temperature drops of 20-30% are not uncommon with systems unable to effectively remove non-condensable gases. From a secondary standpoint, air and other gases create internal oxidation and corrosion that corrode the system from the inside out. As we already know, a major source of air in the system comes from the vacuum breakers which contribute to piping oxidation if the air is not removed. CO2 entrained in steam turn condensate into carbonic acid (H2CO3) when turned into solution if not removed.

These two devices, TAVs and VBs, are frequently confused as to their function. Remember that TAVs primarily expel non-condensable gases and air on startup; and VBs primarily allow air in on shutdown. Their mounting is critical to their successful operation. Observe the following rules for mounting:

• As close to the exchanger as possible on a line with a vertical accumulator, if not on the exchanger itself, opposite the steam supply. 
• Condensate line must be large enough to allow disengagement if horizontal or a vertical accumulator will be needed. If not, the TAV will discharge condensate which means it is not discharging air. The vacuum breaker will spit and leak over time as well. 
• The vertical accumulator is used to provide an accumulation area for non-condensables. It is typically 2” or larger pipe, approximately 2 ft. high if space allows. An isolation valve should be used between the accumulator and the TAV to isolate for maintenance or system air testing. Note that these devices should be excluded from any air test boundaries since the bellows is “balanced,” meaning that steam pressure has a corresponding saturation temperature to “balance” internal pressure of the bellows against external pressure caused by the steam pressure. Air would not allow this balance to take place and would either not close the valve on the air test, or would rupture the bellows if the isolation valve were downstream. 

Since mounting preferences are similar for both vacuum breakers and air vents, a new device has been developed which accomplishes both functions in one device. This is the TAVB-3 which has become standard at a large brewing company.

Article written by Steve Huffman, Mead O'Brien, Inc.

A Look Inside the Neles NDX Intelligent Valve Controller

Neles intelligent valve controller 

Metso’s Neles NDX is the next generation intelligent valve controller working on all single acting control valves and in all industry areas. It guarantees end product quality in all operating conditions with incomparable performance, unique diagnostics, and years of reliable service.

Operating Principle:

The NDX is a 4–20 mA powered micro-controller based intelligent valve controller. The device contains a local user interface enabling configuration and operation without opening the device cover. Configuration and operation can also be made remotely by PC with asset management software connected to the control loop.

After connections of electric signal and pneumatic supply, the micro-controller (μC) continuously reads measurements:

Click for larger view

• Input signal 
• Valve position with contactless sensor (α), 
• Actuator pressure (I) 
• Supply pressure (S) 
• Device temperature

Advanced self­-diagnostics guarantee that all measurements operate correctly.

Powerful micro-controller calculates a control signal for I/P converter (prestage). I/P converter controls the operating pressure to the pneumatic relay (output stage). Pneumatic relay moves and actuator pressure changes accordingly. The changing actuator pressure moves the control valve. The position sensor measures the valve movement. The control algorithm modulates the I/P converter control signal until the control valve position matches the input signal.

The video below demonstrates the NDX's operation. Below the video is the complete installation, maintenance and operation manual for your convenience.

Neles NDX Intelligent Valve Positioner from Mead O'Brien, Inc.

Dampening the Effects of Vibration on Industrial Pressure Gauges

Vibration must be considered
when applying pressure gauges.

Pressure gauges rely on precise and responsive mechanisms to display changes in system pressure as rotational needle movement. By their very nature, these mechanisms are responsive to pulsations within the pressurized system and vibrations that may be evident in the connected piping and structures. The effect of vibration and pulsation is seen as an indicating pointer oscillating rapidly, making a definitive or even useful reading impossible. One solution, applied traditionally, was to fill the gauge with a viscous liquid that would dampen the rapid oscillation of the indicating needle.

While a liquid filled gauge does solve the oscillation problem, it does have a drawback. The liquid in the gauge presents its own set of operational issues requiring consideration in any application.

Provision should be made to check and maintain the liquid level in the gauge
A liquid filled gauge is an additional source of potential leakage in a facility

Ashcroft, a globally recognized manufacturer of gauges for commercial, industrial, and laboratory use, offers a different solution that provides the deflection dampening of a liquid gauge without liquid fill. Available on many of their gauges, the "Plus" option enables stable gauge face display in a dry gauge.

The video below provides a side by side demonstration of a liquid filled and a Plus gauge, so you can see the performance of both types. Share your process gauge requirements and challenges with instrumentation experts, combining your process knowledge with their product application expertise to develop effective solutions.

Boiler Safety in Brewing: Mead O'Brien's Steve Huffman Podcast with Master Brewers Association

Boiler Safety in Brewing

From sanitization to pasteurization, steam heating is critical in the brewing process and steam boilers are one of the most important investments a brewery will ever make. Understanding boiler components and safe boiler operation is crucial to ensuring the protection of people and property, as well as for maximum operating efficiency and optimal energy savings.

This video contains The Master Brewers Association of the Americas (MBAA.com) recent podcast with Mead O'Brien's Steve Huffman about steam boiler safety, operation, and performance.

Mead O’Brien is recognized as leading experts the industrial and commercial use of steam including industrial and commercial boilers, traps, condensate pumps, temperature and pressure controls, heating coils, and heat exchangers.

For more information, visit Mead O'Brien at http://www.meadobrien.com or call (800) 892-2769.

Listen to the discussion below:

Season's Greetings from Mead O'Brien

Season’s Greetings! In warm appreciation of our association during the past year, we extend our very best wishes for a happy holiday season.

May your holidays glitter with unforgettable moments of happiness, laughter, and good cheer.

A Peek Inside an Industrial Centrifugal Separator

A centrifugal separator is a piece of equipment that uses centrifugal force, the force of gravity, and inertia to separate two or more materials. Centrifugal separators work by spinning the material in a chamber at high speed which causes the heavier materials to settle out separately from the lighter materials.

Upon entering the spinning chamber of a centrifugal separator, the spinning force affect materials differently. Heavier materials are more affected by gravity, while lighter materials are affected by inertia. As the materials separate, they are collected in various mechanical or physical ways, such as filtering and screening.

Gases can be purified through the spinning process to remove particulate matter and moisture. The pure gas gas is then be collected as it escapes through the top of the centrifugal separator. Similarly liquids of different weights and viscosities are divided into various chambers in the separator as it moves along.

The Anderson Hi-eF™ Centrifugal Separators operate on a patented two-stage principle of separation that employs carefully controlled flow guiding the entrainment laden vapor through a series of vanes and baffles.  Each component of the separating element is designed to obtain maximum separating efficiency.  Briefly, in the first stage of the separation, impingement against a baffle removes the larger droplets of entrainment. In the second stage of separation, the separator removes the fine mist entrainment by utilizing centrifugal scrubbing action through a uniquely designed contact element.  In each stage, the gas medium and the separated liquid are carefully and continuously guided for maximum efficiency.  The separators are designed to handle large volume flow of a broad range of fluids.  Self-cleaning and engineered without filters or moving parts, the separators are free from maintenance and repair.  For more information visit http://www.meadobrien.com or call  (800) 892-2769.

Watch this video to see an animation of what happens inside the centrifugal separator.

The Application of Limit Switches on Automated Industrial Valves

Limit switch with position indicator.

Limit switches are devices which respond to the occurrence of a process condition by changing their contact state. In the industrial control field, their applications and product variations are almost countless. Essentially, the purpose of a limit switch is to serve as a trigger, indicating that some design condition has been achieved. The device provides only an indication of the transition from one condition to another, with no additional information. For example, a limit switch triggered by the opening of a window can only deliver an indication that the window is open, not the degree to which it is open. Most often, the device will have an actuator that is positively activated only by the design condition and mechanically linked to a set of electrical contacts. It is uncommon, but not unknown, for limit switches to be electronic. Some are magnetically actuated, though most are electromechanical. This article will focus on limit switch designs and variants used in the control and actuation of industrial process valves.

Employed in a wide range of industrial applications and operating conditions, limit switches

are known for their ease of installation, simple design, ruggedness, and reliability. 

Automated valve assembly
including actuator and
limit switch.

Valves, devices used for controlling flow, are motion based. The movable portions of valve trim create some degree of obstruction to media flow, providing regulation of the passage of the media through the valve. It is the movement of critical valve trim elements that limit switches are used to indicate or control. The movable valve trim elements commonly connect to a shaft or other linkage extending to the exterior of the valve body. Mounting electric, hydraulic, or pneumatic actuators to the shaft or linkage provides the operator a means to drive the mechanical connection, changing the orientation or position of the valve trim and regulating the media flow. Because of its positive connection to the valve trim, the position of the shaft or linkage is analogous to the trim position and can be used to indicate what is commonly referred to as “valve position”. Limit switches are easily applied to the valve shaft or linkage in a manner that can provide information or direct functional response to certain changes in valve position.

In industrial valve terms, a limit switch is a device containing one or more magnetic or electrical switches, operated by the rotational or linear movement of the valve.

What are basic informational elements that can be relayed to the control system by limit switches? Operators of an industrial process, for reasons of efficiency, safety, or coordination with other process steps, may need answers to the following basic questions about a process control valve:

• Is the valve open? 
• Is the valve closed? 
• Is the valve opening position greater than “X”? 
• Has the valve actuator properly positioned the valve at or beyond a certain position? 
• Has the valve actuator driven the valve mechanism beyond its normal travel limits? 
• Is the actuator functioning or failing? 

Partial or complete answers to these and other questions, in the form of electrical signals relayed by the limit switch, can serve as confirmation that a control system command has been executed. Such a confirmation signal can be used to trigger the start of the next action in a sequence of process steps or any of countless other useful monitoring and control operations.

Applying limit switches to industrial valve applications should include consideration of:

• Information Points – Determine what indications are necessary or useful for the effective control and monitoring of valve operation. What, as an actual or virtual operator, do you want to know about the real time operational status of a valve that is remotely located. Schedule the information points in operational terms, not electrical switch terms. 
• Contacts – Plan and layout a schedule of logical switches that will provide the information the operator needs. You may not need a separate switch for each information point. In some cases, it may be possible to derive needed information by using logical combinations of switches utilized for other discrete functions. 
• Environment – Accommodate the local conditions and hazards where the switch is installed with a properly rated enclosure. 
• Signal – The switch rating for current and voltage must meet or exceed those of the signal being transmitted. 
• Duty Cycle – The cycling frequency must be considered when specifying the type of switch employed. Every switch design has a limited cycle life. Make sure your selection matches the intended operating frequency for the process. 
• Auxiliary Outputs – These are additional contact sets that share the actuation of the primary switch. They are used to transmit additional signals with specifications differing from the primary signal. 
• Other Actuator Accessories – Limit switches are often integrated into an accessory unit with other actuator accessories, most of which are related to valve position. A visual local indication of valve position is a common example. 

Switches and indicators of valve position can usually be provided as part of a complete valve actuation package, provided by the valve manufacturer or a third party. It is recommended that spare contacts be put in place for future use, as incorporating additional contacts as part of the original actuation package incurs comparatively little additional cost. 

Employing a properly configured valve automation package, with limit switches delivering valve status or position information to your control system, can yield operational and safety benefits for the life of the unit. Good advice is to consult with a valve automation specialist for effective recommendations on configuring your valve automation accessories to maximize the level of information and control.