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THERMODYNAMIC STEAM TRAPS
Aside from the orifice trap this is probably the simplest trap on the market and yet the most widely used. The disc trap is made up of three primary components: the body, the cap and the disc. Like to orifice trap, the operation of the disc trap utilises the difference in specific volume between steam and condensate. With flow moving through a fixed orifice this translates into a difference in velocity between steam and condensate. Operation of the disc trap also utilises flash steam as an operating force to work in conjunction with the velocity of the steam. In order to understand the operation of the disc itself we have to know the principle under which it operates. Bernoulli’s Principle, simply stated: THE PRESSURE OF A FLUID (LIQUID OR GAS) DECREASES AT POINTS WHERE THE SPEED OF THE FLUID INCREASES.
Applying this to the disc trap we are, in fact, creating a low pressure zone between the disc and seats whenever we increase the velocity of the steam or condensate flowing through this zone. In addition, we are providing small chamber for the accumulation of flash steam above the disc. Fig.1 shows a simple disc trap. As flow, in the form on condensate, move into the trap and through the inlet orifice it forces the disc to lift, allowing the condensate to pass through and out the outlet. As the temperature of the condensate reaches its saturation point a percentage of that condensate will flash as it exits the inlet orifice. When steam reaches the inlet orifice two things will immediately happen: the velocity will increase sufficiently to create a low pressure zone between discs and seats pulling the disc down upon the seats. At the same time flash steam will have formed behind the disc and, with the exit orifice sealed off, the pressure induced by this non-escaping flash steam will hold the disc in place. The disc will remain in place until the flash steam has condensed, thus allowing the discs to open again.
Size ½” to 2”. Rating 600# to 2500#
THERMOSTATIC STEAM TRAPS – BALANCED PRESSURE
The Balance Pressure type trap operates on the principal of liquid expansion due to an increase in temperature. The liquid is contained in bellows internal to the steam trap and fixed at one end. Integral to the bellows is a valve attached to its free end. The liquid in the partially filled bellows can be as simple as distilled water under vacuum or an alcohol combination to reduce its vapour point to a lower degree than water. At ambient conditions the bellows are contracted with the valve away from the seat. When steam or condensate, near its saturation point, comes into contact with the bellows the liquid inside the bellows expands and drives the valve into the seat, closing off steam flow.
As the steam condenses, collects and cools, the bellows will cool and contract, backing the valve away from the seat and allowing the accumulated condensate to pass. As the condensate passes through the trap and is replaced by steam the bellows heat up again. As steam comes into contact with the bellows it expands and closes the valve, shutting off flow. As you can see this trap is governed not only by the pressure differential but rather by the temperature of the steam and condensate.
Size ½” to 2”. Rating up to 300#
THERMOSTATIC STEAM TRAPS – BIMETTALIC
Like the Balanced Pressure trap, the Bi-Metallic trap is also governed by temperature variations. However, as the name suggests it does by utilising the differing expansion rates of metals when exposed to temperatures above or below ambient.
By laminating two dissimilar metal strips and exposing the resulting composite to elevated temperatures the differing expansion rates of the composite metal strip will cause it to bow. The higher the temperature the more extreme the bow. The reaction of the Bi-Metal composite is utilised in several different forms with various valve and seat arrangements. The two most widely used designs are variations of the bellows style. One uses Bi-Metal circular discs. The two sets of Bi-Metal laminates are joined at the perimeter with the metal layer of each Bi-Metal disc having the lower rate of expansion facing each other. Several sets of these joined discs may be stacked to increase the force applied when they expand.
Through the center of the stacked discs is a rod, which is attached to the upper most disc. The rod runs through the sets of discs then through a seated orifice. At the end of the rod is a valve. In the relaxed or ambient condition the discs are flat against one another. In their hot condition each set expands against itself causing the bellows to expand. As the bellows expand it draws the valve into the seat of the orifice blocking off the flow of steam.
Size ½” to 8" Class up to 2500#
INVERTED BUCKET STEAM TRAPS
Next to the Disc Trap this is the most widely used trap in the industry. It can arguably be said that this trap is overused. It has such a wide use range that it is probably specified out of misunderstanding in a large number of situations. These aren’t necessarily situations where this type of trap wouldn’t work but rather situations where a less expensive, smaller, possibly longer lasting type of trap could have been applied.
This trap operates with an inverted bucket that floats when steam is present and sinks when condensate exceeds liquid level. When the bucket floats, the valve is closed; when it sinks the valve will open.
This trap is specified based on the differential pressure between the inlet and outlet pressures of the trap. With the length of the valve level fixed the differential pressure is used to determine the weight of the bucket. The result allows the bucket to lift and reset the valve after dumping its condensate. The calculated weight of the bucket also allows the bucket to drop against the upstream pressure when it’s full of condensate.
Size ½” to 2”. Rating up to 1500#
BALL FLOAT AND THERMOSTATIC STEAM TRAPS
As the name implies, the Float & Thermostatic Trap utilises two individual mechanisms that operate in conjunction with one another. The float operates a valve that controls the discharge of condensate. The thermostatic element controls the release of air and CO². The float itself, which is normally a ball type, is located in the lower portion of the trap body. It is attached to a rod which is, in turn, attached to the body of the trap in such a way that it is free to pivot about that point, allowing the float the freedom to move vertically. Near the end where the rod is attached to the body a valve is attached to the rod. The valve is positioned so that when the float is at rest the valve is seated in the outlet on the trap.
The thermostatic element is located in the upper part of the trap body. One end of the element is fixed allowing the opposite end with an attached valve to move in and out of a seated vent discharge opening located in the body of the trap. The vent discharge is connected to the discharge for the condensate. In its relaxed position the valve is pulled away from the seat.
A Ball float can also produced, to eliminate condensate from compressed air and gas and for liquid system.
Size ½” to 4”. Rating up to 600#.