The Burkert Type 3281 direct-acting electromotive 2-way proportional valve is particularly suitable for dosing liquids and gases in closed or open control loops. The valve is driven by a linear stepper motor. The integrated electronics assembly simplifies process integration, meaning additional actuation modules are not necessary. The motor does not need any energy to maintain a certain valve opening. This feature can reduce the energy consumption of a plant dramatically and therefore make it more efficient.

The Type 3281 is available as a variant with an integrated positioner, as well as a variant with an integrated process controller. The valve spindle is rigidly connected to the threaded spindle and driven by the stepper motor, converting rotary movement into linear movement to regulate flow.

Key Features:

• Actuator is not wetted by the medium
• Excellent setting range and fast reaction time
• Connection orifice DN 15
• Medium temperature up to +130 °C
• Variants: positioner, process controller

General Technical Data

Product Properties	Specification
Seal	PTFE
Valve body	Stainless steel
Flow direction	Against closing direction (below seat)
Design	Globe: on/off valve or control valve Angle seat: on/off valve or control valve
Weight	~1.1 kg
Orifice	DN 15, NPS 1/2
Controller variant	On/off valve or position controller or process controller
Dead band of position control	±0.5% (corresponds to setting range 1:100)
Closing time	2.5 s
Operating pressure	0...16 bar(g) (depending on seat size) Vacuum variant up to -0.9 bar(g) (optional)
Duty cycle	Up to 100% (depending on medium and ambient temperature)
Kvs value	0.57...4.55 m³/h
Nominal pressure	PN 25 (DIN EN 1333)
Seat leakage	Class VI (DIN EN 60534-4)
Operating voltage	24 V DC ± 10% (max. residual ripple 10%)
Power consumption	<1 W holding power Max. 12 W (short term 20 W)
Operating medium	Neutral gases and liquids
Medium temperature	-20 °C...+130 °C
Viscosity	Max. 600 mm²/s (cSt)
Degree of protection	IP54

Energy Efficiency

The stepper motor is only supplied with energy when it opens or closes the valve further. Owing to the internal holding torque, the stepper motor only moves when it is controlled. In the remaining time, only the control electronics need a basic voltage supply.

Materials

No.	Element	Material
1	Housing cover	PC (Polycarbonate)
2	Housing base	PPS (Polyphenylenesulfide)

No.	Element	Material
3	Spindle guide	High-performance polymer
4	Sliding washers	High-performance polymer
5	Guide piece	Stainless steel 1.4305
6	O-ring	NBR
7	Compression spring	Stainless steel
8	Spindle seal	PTFE (filled)/FKM, with spring compensation
9	Pipe	Stainless steel 1.4404
10	Body seal	Graphite
11	Spindle	Stainless steel 1.4401
12	Control cone/swivel plate	Stainless steel 1.4571
13	Seat seal	PTFE sealing washer
14	Valve seat	Stainless steel 1.4571
15	Valve body	Stainless steel CF3M/316L

Dimensions

Globe Variant Actuator

A	B	C	D	E	F	G	H	I	J
76	216	188	84	112	52	66	45	58	20

(Dimensions in mm. Twisting of the actuator housing is possible.)

Performance Specifications

Duty Cycle Derating

The duty cycle is an important factor for motor valves. The self-heating of the engine limits the maximum duty cycle. High ambient temperatures additionally increase the risk of damage due to overheating. The following diagram shows the recommended maximum duty cycle as a function of the ambient temperature.

Duty Cycle Limits

Operating the valve outside the recommended duty cycle limits will result in a significantly reduced service life of the valve. The duty cycle refers to the motor, which is only switched on when the valve is to move.

Pressure Range (Standard Variant)

Valve function	Seat size	Controller variant	Port connection	Kvs value [m³/h]	Pressure range [bar(g)]
Globe (Control)	4	Control	G 1/2	0.57	0...16
Globe (Control)	6	Control	G 1/2	1.25	0...16
Globe (Control)	8	Control	G 1/2	1.8	0...12
Globe (Control)	10	Control	G 1/2	2.25	0...7
Globe (On/off)	15	On/off	G 1/2	4.45	0...3.5
Angle-seat (Control)	15	Control	G 1/2	3.6	0...3
Angle-seat (On/off)	15	On/off	G 1/2	4.55	0...3.5

Flow Characteristic

The dimensioning of the seat size is very important for electromotive proportional valves to function properly within the application. The seat size must be selected so that the desired flow range is achieved and, when the valve is fully open, a sufficient portion of the total pressure drop occurs across the valve (Reference value: Δp valve > 25% of the total pressure drop).

Product Operation

Positioner Variant

The proportional valve in the position control variant converts an external standard signal, the position set-point value, into a valve position. The position of the actuator is controlled according to the set-point position. The position sensor records the current position (POS) of the electromotive valve. This actual position is compared by the positioner with the set-point value (CMD) specified as the standard signal. If there is a control difference, a motor control signal is given to the actuator as the actuating variable.

Process Controller Variant

The additionally implemented PID controller can perform not only the actual position control but also a process control in the sense of a cascade control. The process controller is integrated into a control loop. The position setpoint of the valve is calculated from the process setpoint and the actual process value via the control parameters (PID controller).