Armstrong DD-6 Double Duty™ Series steam trap and pump combination offers a low-profile solution to draining heat exchangers in various applications. When there is modulating control on heat exchange equipment, there is a possibility that the system will stall and no longer be able to drain condensate. The Double Duty™ 6 offers the versatility of combining a pump within a steam trap to aid in condensate drainage under all operating conditions, preventing condensate from flooding the heat exchange equipment which can cause corrosion, water hammer, and poor temperature control.

The DD-6 is an ASME code stamped carbon steel vessel. If the condensate floods the body of the Double Duty™ and reaches its upper trip point, high-pressure steam will enter the body and push the condensate out.

Features

• Non-Electric: Uses steam motive with no electricity or special mechanical seals required.
• Compact Design: Low profile for tight space requirements.
• Durable Springs: Inconel X-750 springs for superior service life.
• Robust Vessel: ASME code stamped to 200 psig (available in stainless steel).
• Corrosion Resistant: All stainless steel internals.
• Easy Maintenance: Externally removable vent/motive seats. The pump mechanism is attached to the cap which can be removed from the body without taking it out of the condensate line.

Operation

Operating as a Trap (System Pressure Greater Than Back Pressure)

As the condensate flows through the inlet check valve, the trap and pump floats become buoyant and rise with the fluid level. The upward movement of the float causes the trap valve to open. If the system pressure is greater than the back pressure, the condensate will flow through the steam trap valve into the condensate return.

Operating as a Pump (System Pressure Less Than or Equal to Back Pressure)

If the system pressure is less than the back pressure, liquid floods the body. When the condensate reaches the upper trip point of the pump mechanism, the motive inlet valve opens and the vent valve closes. The open motive valve allows the motive fluid to enter and pressurize the body. The pressure inside the body shuts the inlet check valve and, when it is greater than the back pressure, pushes the water through the discharge check valve into the condensate return line. The float lowers with the water level and when it reaches the lower pump trip point, the motive inlet valve closes and the vent valve opens. This relieves the pressure in the body and allows it to fill again.

Specifications and Materials

Component	Material / Specification
Body	ASME Code Stamped Carbon Steel
Mechanism	Stainless Steel
Float	Stainless Steel
Springs	Inconel X-750
Connections (condensate)	150# Flange
Inlet Check Valve	Optional 1-1/2” (WLC wafer style, carbon steel with SS trim)
Discharge Check Valve	Optional 1” (WLC wafer style, carbon steel with SS trim)
Motive Fluid	Steam
Minimum Motive Differential	10 psi

Physical Data

Dimension	in	mm
“A”	29	737
“B”	16-11/16	424
“C”	1-1/2	38
“D”	1	25
“E”	7/8	22
“F”	1-1/8	28
“G”	2-1/4	57
“H”	24	610
“J”	14	356
“K”	10-13/16	275
“L”	10	254
“M”	2-13/16	71
“N”	8	203
“O”	3-3/16	81
Weight	140 lb	64 kg

Capacities

Pump Capacities

Motive (psi)	Motive (bar)	Back Pressure (psi)	Back Pressure (bar)	Capacity (lb/hr)	Capacity (kg/hr)
15	1	5	0.34	2,400	1,089
25	1.7	5	0.34	3,000	1,361
50	3.5	5	0.34	4,000	1,814
75	5	5	0.34	4,500	2,041
100	7	5	0.34	4,600	2,087
125	8.5	5	0.34	4,700	2,132
150	10.34	5	0.34	4,800	2,177
175	12	5	0.34	4,800	2,177
200	14	5	0.34	4,600	2,087
25	1.7	15	1	2,000	907
50	3.5	15	1	2,800	1,270
75	5	15	1	3,400	1,542
100	7	15	1	3,600	1,633
125	8.5	15	1	3,700	1,678
150	10.34	15	1	3,800	1,724
175	12	15	1	3,600	1,633
200	14	15	1	3,500	1,588
35	2.5	25	1.7	1,800	816
50	3.5	25	1.7	2,300	1,043
75	5	25	1.7	2,900	1,315
100	7	25	1.7	3,000	1,361
125	8.5	25	1.7	3,000	1,361
150	10.34	25	1.7	2,900	1,315
175	12	25	1.7	2,500	1,134
200	14	25	1.7	2,300	1,043
50	3.5	40	3	1,400	635
75	5	40	3	2,000	907
100	7	40	3	2,400	1,089
125	8.5	40	3	2,500	1,134
150	10.34	40	3	2,500	1,134
175	12	40	3	1,800	816
200	14	40	3	1,700	771
75	5	60	4	1,500	680
100	7	60	4	1,800	816
125	8.5	60	4	2,000	907
150	10.34	60	4	1,700	771
175	12	60	4	1,500	680
200	14	60	4	1,400	635

INFO

Published capacities are based on the use of external check valves supplied by Armstrong. Fill head measured from drain point to top of pump case. Discharge per cycle typically 3.5 gallons for DD-6.

Trap Capacities

Differential Pressure (psi)	Differential Pressure (bar)	Capacity (lb/hr)	Capacity (kg/hr)
2	0.14	9,500	4,309
5	0.34	12,400	5,625
10	0.7	15,000	6,804
25	1.7	20,400	9,253
50	3.5	22,500	10,206
75	5.2	22,500	10,206
100	6.9	22,500	10,206
150	10.3	22,500	10,206
200	13.8	22,500	10,206

Capacity Conversion Factors for Other Filling Heads

Filling Head (in)	Filling Head (mm)	Factor
0	0	0.7
6	150	1.0
12	305	1.08
24 or greater	620 or greater	Consult factory

Installation and Maintenance

1. Filling head: Install the DD-6 below the equipment being drained. Fill head is the distance from the top of the cap to the bottom of the receiver. The standard fill head for the DD-6 is 6 inches.
2. Liquid reservoir: Liquid flowing from the heat exchange equipment must be stored during the pump discharge cycle. A liquid reservoir or receiver should be installed above the unit to prevent flooding the equipment.
3. Vent piping: The vent pipe must be pitched to self-drain. The vent connection is 1” NPT.
4. Orientation: The DD-6 must be installed with the vent and motive vertical and the condensate inlet and outlet horizontal. The product will not function properly if not installed in the correct orientation.
5. Connections: Gauge glass connections are ½” NPT and 10” center to center. When connecting pipes, unions or flanges should be used close to the DD-6 connections to reduce maintenance time.

WARNING

Avoid water hammer. If water hammer is experienced it could injure personnel or damage the equipment. Make sure all connections are secure before opening valves. Open valves slowly to reduce the chance of water hammer. Before starting any maintenance make sure the Double Duty™ 6 is completely isolated from the system and at atmospheric pressure.

Troubleshooting

Problem	Diagnosis	Solution
Condensate not discharging	Inlet isolation valve closed	Open valve
	Pump inlet and outlet switched	Re-pipe
	Motive inlet and vent switched	Re-pipe
	Discharge isolation valve closed	Open valve
	Equalizer line isolation valve closed	Open valve
	Motive pressure not adequate	Adjust pressure
	Motive inlet isolation valve closed	Open valve
	Motive strainer clogged	Clean or replace
	Air vent damaged	Replace air vent
	Motive pressure exceeds pump rating	Adjust pressure
	Outlet check valve installed backward	Install check valve properly
	Outlet check valve does not open	Replace
	Inlet check valve does not open	Confirm lack of pressure in body
	Inlet check valve is not completely closed	Disassemble and clean check valve
	Vent valve leaks	Disassemble, clean and inspect - replace defective parts
	Motive steam valve leaks	Disassemble and replace inlet valve
	Float damaged	Disassemble and replace float
Motive steam remains on	Motive steam valve leaks	Disassemble and clean or replace
	Mechanism not assembled properly	Assemble so the motive valve is inserted in motive seat
Steam leaks out of body	Body gasket leaks	Replace gasket
	Plugs leak	Remove, add thread sealer and reinstall