Armstrong's multi-motor pump configurations offer unmatched flexibility for HVAC and hydronic systems that require redundancy, energy savings, and space efficiency. These configurations feature two motors in a shared casing with a single inlet and outlet. Whether you need duty/standby operation, parallel efficiency staging, or a serviceable solution without system shutdown, Armstrong offers three primary product families:

• Twin Pumps (4312, 4392)
• DualArm Pumps (4302, 4382)
• Tango Pumps (4322, 4372, 4332)

Each supports Sensorless Control, with many offering Parallel Sensorless Pump Control (PSPC) for Best Efficiency Staging, delivering up to 30% improved energy performance over traditional methods.

Twin Pumps

Overview

Armstrong Twin Pumps provide two motors in one casing. These are cost-effective, compact, and ideal for simple redundancy. Unlike DualArm or Tango, Twin Pumps do not include internal check or isolation valves.

Note: Where possible, Armstrong Tango Pumps are often the superior choice. They offer more advanced controls, opposite motor rotation for reduced vibration, internal check valves, and — in the case of the 4332 — full isolation valving for live service. When energy savings, reliability, and long-term service access are a priority, Tango pumps are generally recommended.

Models

Model	Flow (USgpm)	Head (ft)	Power (hp)	Size
4312 (Split-Coupled)	Up to 1250	Up to 250	1 to 40	2" to 6"
4392 (Close-Coupled)	Up to 1100	Up to 100	1 to 7.5	2" to 6"

When to Use

• Mid-size systems where external isolation valves are available
• Scheduled downtime is acceptable
• Applications needing basic duty/standby redundancy
• Limited budgets and space constraints

DualArm Pumps

Overview

DualArm pumps include internal diverter or check valves and built-in isolation valves, allowing either motor to be serviced live. Models vary in capacity and power range to meet both large and mid-size commercial needs.

Models

Model	Flow (USgpm)	Head (ft)	Power (hp)	Size
4302 (High Capacity)	Up to 1250	Up to 250	1 to 75	1" to 8"
4382 (Mid-Range)	Up to 1000	Up to 140	0.33 to 7.5	1" to 8"

When to Use

• When service without shutdown is needed
• Ideal for schools, multifamily, and commercial systems
• Sizing flexibility for both small and large GPM ranges
• A good fit where internal valving simplifies installation

Tango Pumps

Overview

Tango pumps add high-end performance features, including opposite motor rotation for vibration reduction, built-in check valves, and in the case of the 4332, suction and discharge isolation valves.

New Tango Enhancements:

• Brand new valve design for full leak-proof operation
• Permanent Magnet (PM) Motors achieving IE5 efficiency for superior energy savings
• Optimized envelope designs, resulting in a smaller footprint compared to most competitors

Models

Model	Flow (USgpm)	Head (ft)	Power (hp)	Size
4322 / 4372	Up to 900	Up to 160	0.25–10	1" to 3"
4332	Up to 2000	Up to 180	15–40	4"

When to Use

• Systems that benefit from vibration reduction and space savings
• Projects requiring built-in live service capability (4332)
• Great for retrofits, tight mechanical rooms, or full parallel control

Sizing Strategy: Duty/Standby vs. Parallel Pumping

Armstrong dual-motor pumps can be configured for two primary strategies:

1. Duty/Standby

One pump operates while the other is idle. The standby pump activates during failure or planned rotation. This strategy ensures uptime but doesn't take advantage of energy savings during part-load conditions.

2. Parallel Pumping with Best Efficiency Staging (via PSPC)

Parallel Sensorless Pump Control (PSPC) is Armstrong’s advanced control strategy that stages pumps based on wire-to-water efficiency, not just speed. It continually evaluates which combination of pumps and speeds delivers required flow at the lowest total energy use.

Here’s how it works:

• Each pump monitors its own speed and power consumption.
• A master controller calculates the most efficient staging—deciding how many pumps should run, and at what speed.
• As system demand changes, PSPC dynamically turns pumps on or off and adjusts speeds to keep the system operating in the optimal part of the efficiency curve.

Even in a configuration with two pumps sized at 50% of total system horsepower, if one pump fails or drops offline, the system can still deliver approximately 80% of the flow and 95% of the heat transfer—thanks to the non-linear relationship between horsepower, flow, and heat exchange.

Key benefits include:

• Up to 30% more energy savings compared to conventional staging
• More stable performance, fewer on/off cycles, and extended equipment life
• No external pressure sensors required (sensorless)
• Efficient redundancy: two 50% pumps for energy savings, or two 100% pumps for full backup

PSPC is ideal for variable load HVAC systems that operate well below peak most of the year, allowing your pump system to stay efficient across all load conditions.

Model Comparison Table

Model	Flow (USgpm)	Head (ft)	Power (hp)	Size Range	Internal Valves	Live Serviceable	Best For
4312 Twin	1250	250	1–40	2"–6"	No	No	Basic redundancy, large commercial
4392 Twin	1100	100	1–7.5	2"–6"	No	No	Budget-friendly, compact installs
4302 DualArm	1250	250	1–75	1"–8"	Yes	Yes	Full serviceability, high flow systems
4382 DualArm	1000	140	0.33–7.5	1"–8"	Yes	Yes	Smaller systems needing redundancy
4322/4372 Tango	900	160	0.25–10	1"–3"	Yes (check only)	No (except 4332)	Compact & efficient HVAC, sensorless apps
4332 Tango	2000	180	15–40	4"	Yes (full ISO)	Yes	High flow, premium redundancy & access