Armstrong WT Series thermostatic wafer steam traps are designed for steam tracing and superheated drip applications. The series features an exclusive non-welded wafer design that eliminates problems associated with weld stress and thin-walled enclosures such as bellows or welded diaphragms, making them highly resistant to water hammer.

Application Note

Since the normal operation of all suppressed temperature-discharge (subcooling) steam traps is to back up condensate, they should not be used on drip legs for saturated steam service, heating, or process equipment. Exercise care in the maintenance of any thermostatic wafer trap with a small discharge area susceptible to clogging.

Models and Features

• WT-1: Ideal for low-capacity steam tracers. Features a sealed stainless steel body and an internal strainer screen two to three times larger than that of other thermostatic traps. Choice of NPT or BSPT screwed connections, or socketweld.
• WT-2000: Equipped with a special 360° connector to expand piping options and simplify installation in any direction. Available with a standard connector, an optional IS-2 stainless steel connector with an integral strainer, or a TVS 4000 trap valve station.
• WT-3: A carbon steel thermostatic wafer trap designed specifically for superheated drip service. It is highly resistant to water hammer and features an internal strainer.

Model WT-1 Trap

Model WT-3 Trap

Model WT-2000 with Standard Connector

Model WT-2000 with IS-2 Connector with Integral Strainer

Specifications and Materials

Feature	WT-1	WT-2000	WT-3
Design	Welded	Welded	Welded
Connections	Screwed (NPT/BSPT), Socketweld	Screwed (NPT/BSPT), Socketweld, Flanged	Screwed (NPT/BSPT), Socketweld
Body & Cap Material	ASTM A240—304L Stainless Steel	ASTM A240—304L Stainless Steel	Carbon Steel C-1018
Capsule Wafer	Hastelloy	Hastelloy	Hastelloy
Capsule Body & Cap	Stainless Steel 303	Stainless Steel 303	Stainless Steel 303
Max Allowable Pressure	28 bar @ 343°C (400 psig @ 650°F)	28 bar @ 343°C (400 psig @ 650°F)	41 bar @ 399°C (600 psig @ 750°F)
Max Operating Pressure	28 bar (400 psig)	28 bar (400 psig)	41 bar (600 psig)

Maximum back pressure: 99% of inlet pressure.

WT Series Capacity

Capacities will vary with the degree of subcooling. When greater capacities are required, the trap will automatically adjust to the load, up to the maximum (cold water) capacity shown, by increasing the amount of subcooling.

Differential Pressure (bar)	Cold Water Start-Up 21°C (kg/h)	Hot Water Start-Up 100°C (kg/h)	Operating Condensate 10°C Below Saturation (kg/h)
0.35	54	45	4.5
0.7	68	77	5.9
1.4	145	113	8.2
2.0	177	136	9.1
3.0	191	159	10.9
3.5	222	181	11.8
5.0	259	218	13.6
7.0	295	263	15.9
10.5	318	318	18.1
14.0	408	363	20.9
17.0	454	431	22.7
21.0	476	465	25.4
24.0	522	544	28.6
28.0	590	567	31.8

Capacities based on differential pressure with no back pressure.

Installation Guidelines

Steam trap installation is critical from both a performance and maintenance aspect. Installation of the trap is simplified if you follow these guidelines:

• Blowdown: Before installing the trap, clean out the line by blowing down at full steam pressure. Blowdown any strainers ahead of the trap.
• Positioning: Install the trap so that it is ACCESSIBLE for inspection and repair, BELOW the drip point, and CLOSE to the vertical drip leg.
• Flow Direction: For proper operation, the trap body must be installed with respect to the flow direction designations on the trap body. Wafer traps may be installed on either vertical or horizontal piping.
• Tracers: On tracer applications, be sure to use only one trap for each tracer line, and be sure that the tracer pitches down to the trap. It is best to insulate the trap as well as the product and tracer line.
• Sealant: Use pipe dope sparingly on male threads only. Leave the end thread exposed to avoid introducing the sealant into the system.
• Strainers & Valves: Install strainers ahead of traps if specified or when dirt conditions warrant their use. Shut-off valves ahead of traps are needed when traps drain steam mains or where the system cannot be shut down for trap maintenance.

Drip Leg Sizing for Superheat Applications

In superheat drip applications (Model WT-3 Only), what little condensate there is usually forms in drip legs to the traps and in the traps themselves, rather than in the main or branch piping. Therefore, providing drip legs of adequate length and diameter is essential to the successful operation of the wafer trap.

Figure 1. Drip Leg Sizing

Figure 2. Trap Draining Drip Leg on Steam Main

Figure 3. Trap Draining Drip Leg at Riser

Drip Leg Recommendation

The properly sized drip leg will capture condensate. Too small a drip leg can actually cause a venturi "piccolo" effect where pressure drop pulls condensate out of the drip leg and trap. Drip leg should be the same as the header diameter up to 4" (100 mm). Above 4" (100 mm), use 1/2 header size, but never less than 4" (100 mm).

Maintenance

High pressure drip traps should be tested at least three times per year. Tracer traps should be tested yearly on applications up to 100 psi (6.8 bar), twice yearly for pressures from 101-450 psi (6.9 - 31 bar), and three times per year for pressures above 450 psi (31 bar).

When the steam trap is suspected of malfunctioning, it can be checked by observing the discharge of the trap. The discharge of a wafer trap is either intermittent or modulating, depending on the load. If the trap is blowing live steam, remove the trap from the line, back flush it with compressed air or water, re-install it and check it again for normal operation.