- Published on Wednesday, 29 May 2013 13:50
- Written by Gerry Longinetti and James Chiu
The main line of defense in combustion devices such as burners and boilers is fuel gas shutoff valves. They are key to safe operation of equipment for nonresidential comfort heating, commercial and industrial heating, and power and steam generation applications.
While conventional modular gas valves are popular and effective, the latest gener-ation of valves has seen dramatic improvements in design. Recent technological advance¬ments offer breakthrough features and benefits. These include higher flows, more compact footprints, and greater modularity and flexibility for downsizing fuel train components. They also include broad¬er temperature ranges, higher close-off pressures, more immediate availability and reduced costs of ownership.
This article explains how OEMs and end users can take advantage of these new designs for a variety of vital applications.
DECIDING TO DOWNSIZE
Some major burner manufacturers have been able to achieve substantially smaller gas trains by using the new valves. This reduction in the size of components has resulted in savings of up to 30% of fuel train component costs. Here’s how that’s happening:
Downsizing via higher flow rates
Using computational fluid dynamics and finite element analysis software, mak¬ers using the new designs have enhanced a valve’s internal geometry and trim weight to maximize flow in as small a size as possible.
For example, a respectable 40% increase in flow rates over older technology has been achieved in solenoid gas valves, where the short stroke makes it difficult to make even minimal gains. In longer stroke electrohydraulic versions, a 100% boost in flow rate is possible (depending on pipe size).
These gains enable OEMs to downsize by, for example, using a 1½-¬inch valve instead of a 2-inch model with the same flow rate. The downsizing doesn’t stop with the valve, either. Designers can specify similarly reduced sizes for the fuel train’s associated manual ball valve, pressure regulator, butterfly valve, and associated piping.
Downsizing with small-footprint designs
Today’s space-constrained burners, boilers or makeup air heaters mean that smaller is usually better. For preassembled units, all elements of the gas train must fit through standard entryways. Even for trains assembled on site, users may need smaller footprints to free up space for production or to provide greater access to other parts of the heating equipment.
A major way in which valve manufacturers have enabled component downsizing is by pro¬viding flanged end connections for space-saving, face-to-face mounting. This eliminates the need for pipe nipples when joining two valves in series and provides the smallest face-to-face, double-valve footprint.
Downsizing despite low supply pressure
Designers of gas-fired combustion systems for use in many North American cities face a special challenge: low supply pressure. Across New York City, for example, many gas mains provide supply pressure under 10 inches of water column (IWC). In a typical installation, designers must balance the available supply pressure against the pressure drop or pressure the heating equipment and the related components in the fuel supply train consume.
Where supply pressure is minimal, designers must compensate either by including a gas booster device, which is an added expense to the customer, or by over-sizing piping and components in the gas train, adding considerable space, inefficiency and cost.
The high flow rates of modular gas valves require lower pressure drops. For example, at 2 IWC inlet pressure and 1 IWC drop, one of the newer 1½-inch gas valves could offer almost twice the flow of previous technology, which nets 3 million British thermal units per hour (Btu/hr) versus 1. 7 million Btu/hr.
CHOOSE THE MOST FLEXIBLE TECHNOLOGY
Modular gas valve purchasers can choose from two basic valve operating technologies and can mix and match the components for design. The two technologies include solenoid and electrohydraulic.
Solenoid valves work electromechanically with electrical current running through a solenoid coil to magnetically actuate valve opening or closing. Electrohydraulic valves work by converting electrical current into hydraulic flow to actuate opening or closing.
With configurations that include double solenoid, solenoid and electrohydraulic and double electrohydraulic, it is possible to fine-tune the valve array to fit precise application needs. Other advantages of modular gas valve designs include:
Simple installation and maintenance
Until recently, manufacturers of gas shutoff valves offered no choice in mounting options. Both monobloc and modular versions required adding adaptors to their flanges to connect to piping.
A new option is available with dual end connections. Where customers prefer to simplify subsequent valve removal, avoid pipe unions, and minimize maintenance downtime, the usual flange adaptors are available. However, for those who want to eliminate the expense of adaptors, valve bodies can also be internally threaded through national pipe thread taper for direct “hard-pipe” mounting.
Broad temperature ranges
Many gas shutoff valves must function in a wide variety of environmental conditions that offer an equally wide variety of challenges. For instance, a building in the northern latitudes of the world, such as Minnesota or the provinces of Canada, may have valves installed in a boiler room that stays hot year-round. However, the same building also may have valves in a rooftop makeup air unit that sees extremely cold temperatures on frigid winter nights. Formerly, users were forced to purchase and stock multiple sets of valves rated for different temperatures.
Modular gas valves designed with wider ambi¬ent temperature ranges can reduce bloated inventories. The designs include products rated for operation down to -40°F (-40°C) and up to 140°F (60°C) for solenoid models and up to 150°F (66°C) for electrohydraulic valves.
Higher close-off pressures
In many locations, the gas supply entering a site is pressurized to about 30 psi. Additionally, a primary regulator and sometimes a secondary regulator upstream of the safety valve reduce the gas going to the gas train and heating equipment to 5 psi or below. Conventional modular gas shutoff valves usually carry maximum operating pressure differential ratings of 5 psi, which means they can safely open and close against that amount of line pressure. However, unexpected spikes in gas supply pressure hold the potential to rupture the regu¬lator’s diaphragm, which could lead to an overpressure condition and unsafe combus¬tion.
Valves designed with a high close-off pressure rating, typically 50 psi, will close against gas pressure upstream of the regulator up to the valves’ close-off pressure rating. This rating is important because if the upstream regulator ruptures, the high gas pressure would trip the high gas pressure limit switch, calling for the main gas shutoff valves to close. An overpressure protection device, such as a pressure relief valve, needs to be installed if the gas valves do not have a close-off pressure rating higher than the line pressure upstream of the regulator.
Incorporating valves with a close-off pressure rating greater than the building supply pressure eliminates the effort and expense of relief devices.
When selecting a modular gas shutoff valve for a given piece of combustion equipment, consider the flow rates, space requirements, mounting options, temperature ranges and close-off pressures. The right choice can reduce cost of ownership, reduce time and costs for installation and maintenance, decrease inventories and open up valuable space in your facility.