BURKERT 348394 (Type 2031) is an externally piloted pneumatic piston actuator designed for 2/2-way diaphragm valves with a body nominal size of DN25 (diaphragm size 25). Built with a polyphenylene sulphide (PPS) housing and internal FKM fluor rubber piston seals, this actuator operates under Control Function A (normally closed by spring force). The control air interface uses a standard internal G 1/4 thread, engineered to operate reliably across a pilot pressure range of 5.5 to 7.0 bar. The PPS actuator construction withstands ambient operating temperatures from +5 °C to +140 °C, offering compatibility with clean-in-place (CIP) and sterilisation-in-place (SIP) regimes.

Type 2031 CLASSIC actuators transfer mechanical force via a spindle connected to an internal piston directly into the diaphragm compressor. An integrated optical position indicator located inside a transparent polysulfone (PSU) cap provides local visual feedback of valve open and closed states. The compact PPS variant is autoclavable and supports modular automation through direct mounting interfaces for electrical position indicators, including Bürkert Type 8690 and Type 8697.

Technical Data and Operational Limits

Article 348394 defines the actuator assembly matching DN25 diaphragm valve bodies across forged stainless steel (VS), cast stainless steel (VG), stainless steel tube (VP), and engineered plastic valve bodies.

Technical Attribute	Specification
Product Identity	Bürkert Article 348394 (Type 2031 CLASSIC)
Valve Construction	Pneumatic piston actuator for diaphragm valve
Body Nominal Size / Diaphragm Size	DN 25 (Diaphragm size 25 mm)
Actuator Size	80 mm diameter (Size F)
Actuator Material	Polyphenylene sulphide (PPS)
Piston Seal Material	FKM (Fluor rubber)
Control Function	Control Function A (Normally closed by spring force)
Pilot Air Port	G 1/4 internal thread
Pilot Pressure Range	5.5 bar to 7.0 bar
Ambient Temperature Range	+5 °C to +140 °C
Fluidic Connection Ports	2 ports (2/2-way on/off valve operation)
Cleaning Capabilities	CIP capable, SIP capable, autoclavable
Inspection Certificate 3.1	No
Factory Certification 2.1 Membrane	No

INFO

For diaphragm size 25 combined with an 80 mm (Size F) actuator in Control Function A, the minimum required pilot pressure is 5.5 bar at 0 bar line operating pressure, dropping to 4.5 bar when opposing maximum line working pressure.

Medium Pressure Ratings for DN25 Valve Assemblies

When fitted to compatible Type 2031 DN25 valve bodies, actuator size 80 mm (Size F) provides the following working pressure ratings under Control Function A:

Diaphragm Material	Maximum Static Operating Pressure	Maximum Dynamic Operating Pressure
EPDM (AD), FKM (FF)	10 bar	10 bar
PTFE/EPDM (EA), Advanced PTFE (EU), GYLON® laminate (ER)	10 bar	7.5 bar

Static tightness defines the closed valve state where test pressure is applied to one side of the body seat with zero seat leakage. Dynamic tightness defines the closing capability against fluid actively flowing through the valve with backpressure on both sides of the seat.

Actuator Construction and Material Specifications

Type 2031 CLASSIC actuators sized 40 mm to 125 mm use corrosion-resistant polymers and stainless steel internal components:

Item No.	Element	Material
1	Transparent cap	Polysulfone (PSU)
2	Actuator cover	Polyphenylene sulphide (PPS standard)
3	Pilot air ports	Stainless steel 1.4305
4	Piston seal	FKM fluor rubber
5	Socket	Sinter metal
6	Interface	Polyphenylene sulphide (PPS standard)
7	Diaphragm	EPDM (AD), PTFE/EPDM (EA), Advanced PTFE/EPDM (EU), GYLON® laminate (ER)
8	Valve body	Forged 1.4435/316L (VS), cast 1.4435 (VG), tube 1.4435-BN2 (VP), or plastic (PP/PVDF/PVC)

Actuator Dimensions

For diaphragm size 25 with actuator size 80 mm (Size F), the CLASSIC actuator features the following standard dimensions:

Configuration	Actuator Size ∅	Outer Diameter ∅ A [mm]	Lower Clearance C [mm]	Pilot Port K	Height H [mm]
Standard CLASSIC Actuator	80 mm (F)	101	60	G 1/4	156
CLASSIC with MT85 Block Interface	80 mm (F)	101	60	G 1/4	190
CLASSIC with Type 8697 Control Unit	80 mm (F)	101	60	G 1/4	252 (HM), 286 (HM + MT85)

Installation and Valve Body Assembly

Installation of actuator 348394 onto the valve body requires strict adherence to assembly sequences to prevent diaphragm pinch damage and maintain leak-tight operation.

Assembly Procedure for Control Function A

1. Ensure the internal compressor is aligned correctly in the guide slots.
2. Apply compressed air to the lower pilot air port (8) at 5.5 to 7.0 bar to retract the piston and open the valve.
3. Position the actuator and diaphragm squarely onto the valve body.
4. Thread the body screws (11) crosswise by hand until the diaphragm is uniformly seated between the body and actuator interface without full compression.
5. Cycle the valve twice using pilot air to seat the elastomer evenly.
6. Depressurise and vent the pilot air connection.
7. Tighten body screws crosswise in three stages (approximately 1/3, 2/3, and full target torque) without pilot pressure applied.

Body Reinforcement on Plastic Bodies

When mounting this actuator on polypropylene (PP) valve bodies in sizes DN15, DN20, or DN25, the designated metal body reinforcement plate is mandatory to prevent body distortion under bolting torque.

Diaphragm Size	Forged (VS), Cast (VG), Plastic (PP/PVC/PVDF) Body Torque	Tube Body (VP) Torque
DN 25 — EPDM / FKM Diaphragms	5.0 Nm (+10% tolerance)	7.0 Nm (+10% tolerance)
DN 25 — PTFE / Advanced PTFE / GYLON®	6.0 Nm (+10% tolerance)	8.0 Nm (+10% tolerance)

Diaphragm Attachment on DN25

Diaphragm size 25 uses a threaded connection for EPDM, FKM, and GYLON® diaphragms, whereas PTFE diaphragms utilize a 90° bayonet lock. When installing threaded diaphragms, screw the stud hand-tight into the compressor and loosen it by one half-turn counter-clockwise before resting it on the body weir. Ensure the identification tab is positioned perpendicular to pipeline flow.

Maintenance, Spare Parts, and Conversion

The Type 2031 pneumatic actuator requires no routine lubrication if operated within specified conditions. Wearing parts consist of the piston and spindle seals and the process diaphragm. Regular inspection of the bonnet relief bore is recommended; any medium escaping from the relief bore indicates diaphragm wear.

Body screws should be retorqued crosswise after the initial steam sterilisation cycle. Inspect the diaphragm for wear at or before 100,000 switching operations.

Spare Parts for Actuator Size 80 mm (F) and DN25 Diaphragms

Component Description	Material Code / Details	Article Number
Actuator Seal Set	FKM seals for PPS Actuator Size 80 mm (F), DN20/25	011492
EPDM Diaphragm	EPDM (AD) / Material code EPDM E04, DN25	688424
FKM Diaphragm	FKM (FF) / Material code FKM F01, DN25	677687
PTFE/EPDM Diaphragm	PTFE/EPDM (EA) / Material code EPDM E04/PTFE P05, DN25	20093071
Advanced PTFE Diaphragm	Advanced PTFE (EU) / Material code EPDM E04/PTFE P06, DN25	20093082
GYLON® Laminate Diaphragm	GYLON® / EPDM (ER) / Material code PTFE L08, DN25	693178
Conversion Kit CF A to CF B	Spring and O-ring set for Actuator Size 80 mm (F)	011689
Conversion Kit CF A to CF I	O-ring set for double-acting Actuator Size 80 mm (F)	011767
Actuator Cover Wrench	Service wrench for ∅ 80 mm cover	639171

Preloaded Springs Hazard

Actuators configured in Control Function A contain preloaded compression springs. When opening the actuator cover (2) with service wrench 639171 for seal replacement or conversion, hold the assembly securely to prevent personal injury from springing internal components.

Combination with Control Units and Automation

Actuator 348394 integrates with electrical position feedback units to form automated valve blocks:

• Bürkert Type 8697: Compact position feedback indicator designed for integrated mounting onto CLASSIC series actuators. Features IP65/IP67 enclosure, mechanical or inductive limit switches, LED status indicators, and optional IECEx intrinsic safety.
• Bürkert Type 8690: Decentralised pneumatic control unit for direct automated valve pilot actuation.
• CLASSIC Valve Systems: Pairing actuator 348394 and a Type 2031 body with Type 8697 creates the factory-tested Bürkert Type 8801-DB on/off valve system.