SAN-EI Air Motor

DM Series – Radial Piston Type Air Motor

The DM Series air motor is a radial piston type pneumatic motor manufactured by SAN-EI SEIKI SEISAKUSHO Co., Ltd. (Japan). It is designed for applications requiring low speed, high torque, and long service life.

Compared with vane type air motors, the DM series provides strong starting torque and stable operation under heavy load, making it suitable for equipment such as hoists, winches, and other industrial machinery requiring powerful drive performance.

1 Structure and Working Principle

The DM series adopts a radial piston structure.

Mechanical principle

Multiple pistons are arranged radially around the crankshaft.
Compressed air pushes each piston outward.
The piston force is transmitted to the crankshaft through connecting rods.
A rotary valve synchronized with the crankshaft distributes compressed air to each cylinder.

This mechanism converts compressed air energy into rotational motion of the motor shaft.

The radial piston design provides higher torque output than vane-type motors, especially at low rotational speeds.

2 Main Features

Low Speed – High Torque

The DM series provides large torque in the low-speed range, making it ideal for equipment that requires strong starting force.

Durable and Long Service Life

These motors have been used in industrial applications for many years and are known for their durability.

Multiple Configuration Options

The motor can be supplied with optional equipment such as:

Brake units
Gear reducers
Control valves

This flexibility allows adaptation to different industrial systems.

Strong Engine Braking

When used in a meter-out speed control circuit, the motor can provide strong engine braking capability.

Flexible Installation

Two mounting options are available:

Base mounting
Flange mounting

3 Lubrication System

The DM series uses an oil-bath lubrication system for internal moving parts.

Advantages:

Stable lubrication performance
Reduced wear on sliding components
Longer service life

A line lubricator is normally not required, but it is recommended for:

continuous operation
infrequent operation
vertical installation (shaft downward)

4 Installation Notes

SAN-EI provides several operational recommendations:

The motor should normally be installed horizontally.
If vertical installation is required, consultation with the manufacturer is recommended.
Flexible piping should be used for air supply and exhaust connections.
Oil levels must be checked regularly using the oil gauge.

For motors equipped with brakes, a center-open type control valve must be used to ensure proper brake release.

5 DM Series Models and Specifications

Specifications below are based on 0.5 MPa air pressure.

Model	Output	Speed	Torque	Air Consumption
DM1	0.64 kW	1300 rpm	4.7 Nm	0.7 m³/min
DM3	1.4 kW	1250 rpm	10.9 Nm	1.7 m³/min
DM9	3.1 kW	1000 rpm	30.0 Nm	3.4 m³/min
DM220	6.0 kW	645 rpm	89.0 Nm	4.8 m³/min
DM36	9.7 kW	630 rpm	148.0 Nm	7.5 m³/min
DM45	14.2 kW	800 rpm	170.0 Nm	14.0 m³/min

From these specifications it can be seen that the DM series covers a wide range of torque and power outputs, from small machines to heavy-duty industrial equipment.

6 Typical Applications

The DM series is commonly used in industries requiring high torque pneumatic drives.

Hoisting Equipment

Air hoists
Winches

Marine Equipment

Deck machinery
Mooring equipment

Mining and Heavy Industry

Conveyors
Drilling equipment

Industrial Machinery

Mixers
Agitators
Large industrial drive systems

Because air motors use compressed air instead of electricity, they are suitable for explosive or hazardous environments.

7 Advantages Compared with Electric Motors

Air motors like the DM series provide several benefits:

Safe in explosive atmospheres
No risk of electrical spark
Overload protection (motor slows or stops safely)
Instant start and stop
High torque at low speed

These advantages make them popular in chemical plants, offshore facilities, and hazardous industrial areas.

※給気圧力0.5MPa時
型式	出力［kw］	回転数［rpm］	トルク［N-m］	空気消費量［㎥/min(nor)］
DM1	0.64	1300	4.7	0.7
DM3	1.4	1250	10.9	1.7
DM9	3.1	1000	30.0	3.4
DM220	6.0	645	89.0	4.8
DM36	9.7	630	148.0	7.5
DM45	14.2	800	170.0	14.0

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San-ei Air motor DM Series