BURKERT 312308 (Type 3285) is an electromotive 2-way globe proportional valve designed for continuous fluid dosing and control of neutral gases and liquids. Driven by an integrated stepper motor, the valve regulates flow through precision ceramic control discs without requiring an external actuation control module. The stepper motor draws no electrical power in holding position, consuming less than 1 W when resting at any intermediate set-point stroke.

Article 312308 is configured with a stainless steel 1.4408 valve body, female G 3/4 port connections, a nominal seat diameter of 12 mm (7/16"), and an oxide ceramic disc seat sealed with FKM. It delivers a water flow coefficient (Kvs) of 3.9 m³/h across an operating pressure span of 0 to 6 bar(g). The integrated positioner module interfaces directly with digital fieldbus automation via the Bürkert system bus (büS) on a 5-pin M12 connector.

Technical Specifications

Specification Parameter	Value for Article 312308	Type 3285 Series Range
Port connection 1	G 3/4 internal thread	G, NPT, Rc (1/2" to 1")
Orifice size / Seat diameter	DN 12 mm (7/16")	DN 8 mm to DN 25 mm
Flow coefficient Kvs (water)	3.9 m³/h	1.8 m³/h to 9.6 m³/h
Nominal pressure range	0...6 bar(g)	0...6 bar(g) (vacuum to -0.9 bar optional)
Fluid medium	Neutral gases and liquids	Neutral gases and liquids
Medium temperature range	0 °C...+70 °C	-30 °C...+70 °C (EPDM), 0 °C...+70 °C (FKM, NBR)
Ambient temperature range	-10 °C...+60 °C	-10 °C...+60 °C
Operating voltage	24 V DC ±10% (max. 10% ripple)	24 V DC ±10%
Power consumption	< 1 W holding, max. 12 W moving	< 1 W holding, max. 12 W moving
Dead band of position control	±0.5% (setting range 1:100)	±0.5% (setting range 1:100)
Closing time	4 s	4 s
Protection class	IP50	IP50
Flow direction	Above seat	Above seat
Fluid viscosity	Max. 80 mm²/s (cSt)	Max. 80 mm²/s (cSt)
Valve body material	Stainless steel 1.4408	Brass, Stainless steel 1.4408
Seat seal material	Oxide ceramics / FKM	Oxide ceramics / FKM, EPDM, NBR
Control variant	Digital fieldbus positioner	Standard On/Off, Standard Control, Positioner, Process Controller

Materials of Construction

The actuator assembly is completely isolated from the fluid flow path. The internal fluidic shut-off and metering mechanism relies on high-purity technical ceramics to achieve wear resistance during continuous modulation.

Item No.	Component Element	Material Specification (Article 312308)	Alternative Series Materials
1	Housing cover	Polycarbonate (PC)	PC
2	Housing base	Polyphenylene sulphide (PPS)	PPS
3	Spindle	Stainless steel 1.4404 / 1.4401	Stainless steel 1.4404 / 1.4401
4	Spindle seal	FKM	EPDM, NBR
5	Disc	Technical ceramics	Technical ceramics
6	Valve seat	Technical ceramics	Technical ceramics
7	Valve body	Stainless steel 1.4408	Brass
8	O-ring	FKM	EPDM, NBR
9	O-ring	FKM	EPDM, NBR
10	Parallel pin	Stainless steel 1.4401	Stainless steel 1.4401
11	Spring	Stainless steel / spring steel	Spring steel / stainless steel

Dimensional Specifications

Dimensions for Type 3285 threaded variants are listed in millimeters (mm). Article 312308 corresponds to the G 3/4 thread row:

Thread Standard	Connection D	A (mm)	B (mm)	C (mm)	E (mm)	F (mm)	G (mm)	H (mm)
NPT (ASME B 1.20.1)	NPT 1/2	8.2	13.7	—	97.0	138.0	31.0	58.0
Rc (ISO 7-1)	Rc 1/2	—	13.7	—	97.0	138.0	31.0	58.0
G (EN ISO 228-1)	G 1/2	—	—	14.0	97.0	138.0	31.0	58.0
NPT (ASME B 1.20.1)	NPT 3/4	8.6	14.0	—	103.5	147.0	43.0	80.0
Rc (ISO 7-1)	Rc 3/4	—	14.0	—	103.5	147.0	43.0	80.0
G (EN ISO 228-1) [312308]	G 3/4	—	—	16.0	103.5	147.0	43.0	80.0
NPT (ASME B 1.20.1)	NPT 1	10.2	16.8	—	108.5	156.5	49.0	95.0
Rc (ISO 7-1)	Rc 1	—	16.8	—	108.5	156.5	49.0	95.0
G (EN ISO 228-1)	G 1	—	—	18.0	108.5	156.5	49.0	95.0

Electrical Control and büS Interface

Article 312308 operates as a digital fieldbus positioner valve variant. It communicates over the Bürkert system bus (büS) based on CANopen protocols using an A-coded 5-pin M12 circular plug.

Pin Assignment for Digital Fieldbus (büS)

Pin Number	Signal Configuration	Description
1	Shield	Cable shield connection
2	24 V DC	Main power supply (+24 V DC ±10%)
3	GND	Power supply ground (0 V)
4	CAN_H	CANopen / büS communication high line
5	CAN_L	CANopen / büS communication low line

Pin Assignment for Analogue and Process Controller Variants

Standard analogue positioner versions utilize an 8-pin A-coded M12 connector (Pin 1: 24 V DC, Pin 2: GND, Pins 3–5: internal büS parameterization, Pin 6: Set-point input +, Pin 7: Actual value output, Pin 8: Signal GND). Dual-loop process controller variants (D) feature an additional 5-pin M12 socket for an external 4...20 mA, 0...10 V, or frequency process transmitter input.

Operating Performance and Derating

Motor duty cycle designates the operating time of the stepper drive during position changes, rather than total device power-on time. The motor switches on only when traversing between stroke positions.

Operating Limits and Duty Cycle

Stepper motor self-heating limits continuous adjustment cycles. High ambient temperatures increase internal thermal stress. Exceeding recommended duty cycle limits accelerates wear and reduces valve operating life. In energy-saving mode with reduced driving force, higher duty cycle limits apply.

Pressure Range and Flow Characteristics

Type 3285 proportional valves maintain a linear flow characteristic when correctly sized against the piping system hydraulic resistance. Seat sizes range from 8 mm to 25 mm:

Valve Function	Seat Size (DN)	Port Connection	Kvs Value Water (m³/h)	Operating Pressure [bar(g)]
Control valve	8	G 1/2	1.8	0...6
Control valve	10	G 1/2	2.5	0...6
Control valve [312308]	12	G 3/4	3.9	0...6
Control valve	15	G 3/4	5.4	0...6
Control valve	20	G 1	8.1	0...6
Control valve	25	G 1	9.6	0...6

Determination of Flow Coefficient (Kv)

Kv calculations determine required valve flow capacities based on pressure drop conditions:

Flow Condition	Kv Value for Liquids (m³/h)	Kv Value for Gases (m³/h)
Sub-critical: $p_2 > \frac{p_1}{2}$	$K_v = Q \cdot \sqrt{\frac{\rho}{1000 \cdot \Delta p}}$	$K_v = \frac{Q_N}{514} \cdot \sqrt{\frac{T_1 \cdot \rho_N}{p_2 \cdot \Delta p}}$
Supercritical: $p_2 < \frac{p_1}{2}$	$K_v = Q \cdot \sqrt{\frac{\rho}{1000 \cdot \Delta p}}$	$K_v = \frac{Q_N}{257 \cdot p_1} \cdot \sqrt{T_1 \cdot \rho_N}$

Valve Sizing Recommendation

Select the seat size so that at maximum flow rate, the pressure drop across the fully opened valve represents at least 25% of the total system pressure loss (Δp_valve > 0.25 · Δp_total). A nominal Kvs value approximately 10% higher than the calculated operating Kv prevents characteristic distortion.

Product Operation and Positioner Control Loop

In the positioner configuration, the internal position controller continuously evaluates the digital set-point command (CMD) transmitted over the büS network against the actual stroke position (POS) reported by the integrated non-contact position sensor. If a control deviation (Xd1) occurs, the electronics drive the stepper motor to reposition the ceramic control disc until the deviation drops within the ±0.5% dead band. Integrated status LEDs indicate current operating states and physical valve travel end positions.

Capacitive Buffer Module and Failsafe Options

Type 3285 valves do not contain mechanical return springs. To secure a designated safety position upon power supply failure, the valve must be powered through the optional Type 1573 capacitive buffer module.

Pin Number	Buffer Module Pin Configuration
1	Shield
2	24 V DC (Power Input)
3	GND
4	CAN_H
5	CAN_L

Upon loss of main line power, the buffer module provides an 18 V DC auxiliary voltage for several seconds. The valve electronics detect the voltage drop and drive the stepper motor to the configured safety shut-off position. Up to two Type 3285 valves can be supported by a single capacitive buffer module.

Software Configuration and Integration

Parameter configuration, diagnostic logging, and calibration are performed via the Bürkert Communicator software tool (EDIP environment). Connection to a service PC requires an optional USB-büS interface stick:

• Connect the büS stick directly to the M12 5-pin fieldbus plug.
• Activate the terminating resistor on the büS stick unless connecting into a pre-terminated network.
• Use the graphical tool to adjust control parameters, invert direction of action, set safety positions, and monitor cyclic process data.

Compatible Accessories Ordering Chart

Standard Power and Buffer Accessories

Accessory Description	Article Number
Power supply unit Phoenix Class 2 (Type 1573), 85...240 V AC / 24 V DC, 1.25 A, NEC Class 2	772438
Power supply unit for DIN rail (Type 1573), 100...240 V AC / 24 V DC, 1 A, NEC Class 2	772361
Power supply unit for DIN rail (Type 1573), 100...240 V AC / 24 V DC, 2 A, NEC Class 2	772362
Power supply unit for DIN rail (Type 1573), 100...240 V AC / 24 V DC, 3.8 A, NEC Class 2	772898
Capacitive buffer module (Type 1573) for safety shut-off position during power failure	773440

Connection Cables

Cable Description	Article Number
M12 circular socket with cable, 8-pin, 2 m pre-assembled cable for analogue variants	919061
M12 circular socket with cable, 8-pin, 2 m pre-assembled shielded cable for analogue variants	918991
M12 cable shielded, 5-pin, 2 m pre-assembled cable for process actual value input signals	559177

Bürkert Communication Accessories

Communication Accessory Description	Article Number
Bürkert Communicator software tool	Type 8920
büS adapter, M12 socket 8-pin to M12 plug 5-pin	773286
USB-büS interface set 1 (Type 8923) with M12/micro-USB cables, terminating stick, and software	772426
USB-büS interface set 2 (Type 8923) with M12 cables, Y-distributor, and büS stick (0.7 m cable)	772551