BURKERT 325990 is a Type 6407 servo-assisted 2/2-way piston valve configured with circuit function A (normally closed), an internal thread G 3/4 process port, and a DN 20 nominal orifice. The valve employs a rigid mechanical coupling between the pilot valve plunger and the main piston, enabling full opening without any minimum differential pressure across the 0 to 10 bar operating span. Built with a brass valve body, a stainless steel seat insert, and a PTFE/graphite sealing combination, article 325990 is designed for neutral gases, liquids, and steam within a fluid temperature range of -40 °C to +150 °C.

The electromagnetic actuation system utilizes a 42 mm epoxy-encapsulated coil (Class H thermal insulation) rated for 110 V AC at 60 Hz. The welded connection between the core guide tube and the stopper provides pressure containment and leak tightness. When paired with an approved DIN EN 175301-803 Form A cable connector, the assembly achieves an IP65 ingress protection rating.

Circuit Function and Operating Principle

Article 325990 operates according to circuit function A as a 2/2-way normally closed valve with fluid inlet at port 1 (P/NC) and flow directed above the seat.

Circuit Function A Details

In the de-energized state, spring force and medium pressure act on the piston to seal the main orifice shut. When the solenoid coil is energized, the plunger lifts and unseats the pilot orifice while mechanically pulling the piston upward through the fixed coupling. This mechanism allows the valve to open fully even at 0 bar differential pressure.

Technical Specifications

Specification Parameter	Value / Description
Valve Type	6407
Article Number	325990
Circuit Function	CF A (2/2-way, normally closed)
Port Connection	G 3/4 internal thread
Nominal Orifice	DN 20 (20 mm)
Pressure Range	0.00...10.00 bar (0...1.0 MPa)
Flow Rate Kv (Water)	5.7 m³/h (measured at +20 °C, 1 bar delta-P)
Flow Rate QNn (Gas)	6100 l/min
Operating Voltage	110 V AC (60 Hz)
Voltage Tolerance	±10%
Coil Size	42 mm (Size K)
Inrush Power (AC)	150 VA
Holding Power (AC)	41 VA / 16 W
Duty Cycle	100% continuous operation
Switching Time (Opening)	30 ms (measured at +20 °C, 6 bar)
Switching Time (Closing)	250 ms (measured at +20 °C, 6 bar)
Fluid Viscosity	Max. 21 mm²/s (21 cSt)
Medium Temperature	-40 °C...+150 °C
Ambient Temperature	Max. +45 °C
Body Material	Brass
Seat Material	Stainless steel
Seat Seal / Outside Seal	PTFE / Graphite
Electrical Connection Sort	Plug pattern Form A acc. to DIN EN 175301-803
Protection Class	IP65 with mounted cable plug
Overall Face-to-Face Length	100 mm

Material Specifications

Item No.	Element	Material Designation
1	Coil	Epoxy
2	Stopper	Stainless steel 1.4113 / AISI 434
3	Spring	Stainless steel 1.4310 / AISI 301
4	Armature guide tube	Stainless steel 1.4303 / AISI 305 / 308
5	Core (Armature)	Stainless steel 1.4113 / AISI 434
6	Cover	Brass
7	Seal	PTFE
8	Piston ring	PTFE
9	Sealing ring	Graphite
10	Plunger	Brass
11	Piston seal	PTFE
12	Valve body	Brass (seat in stainless steel)

Dimensional Data

Dimensions for Type 6407 standard brass threaded body variants DN 13 through DN 32:

DN	Port Thread	A1 [mm]	B1 [mm]	Thread Depth F1 [mm]	Body Width E1 [mm]	Length L1 [mm]	Wrench Size SW [mm]
13	G 1/2	118.7	132.7	14.0	40	65	27
20 (325990)	G 3/4	119.7	135.7	16.0	60	100	32
25	G 1	125.7	146.2	18.0	70	115	41
32	G 1 1/4	142.7	167.7	20.0	85	126	50
32	G 1 1/2	146.7	176.7	22.0	85	126	60

Coil dimensions for Size K (42 mm width, standard on DN 20 AC):

• M (coil width): 42 mm
• N (coil offset to centerline): 27 mm
• O (coil height): 55.5 mm

Installation and Piping Guidelines

Piping Cleanliness and Protection

Before piping installation, clean all connecting lines of scale and debris. Install a dirt trap upstream of the valve inlet with a mesh size of ≤ 500 µm to protect internal orifices and pilot passages from clogging.

1. The valve may be mounted in any orientation, preferably with the actuator upright.
2. Note flow direction: an arrow cast into the valve body indicates the medium flow vector.
3. Hold the valve body directly using an open-end wrench (SW 32 mm for DN 20) during threaded connection; do not use the solenoid coil as a lever arm.
4. Avoid pipe strain on the valve housing, and verify that thread sealant cannot enter the internal fluid passages.

Electrical Safety

Disconnect electrical power before connecting wiring or dismounting components. Secure the main circuit against unintentional reactivation. Always attach the protective grounding conductor (PE) and check continuity between the solenoid coil and the valve body.

When securing the cable plug to the terminal prongs, tighten the center fastening screw to a maximum torque of 1 Nm to preserve the seal compression without stripping threads.

Maintenance, Solenoid Installation, and Tightening Torques

Solenoid Operation Precaution

Never energize the solenoid coil unless it is fully installed on the armature guide tube. Powering an unmounted coil causes rapid overheating and coil burnout.

When reinstalling the coil on the core tube, position the coil over the tube until firmly seated against the valve cover, then torque the retention nut with an open-end wrench. Do not continue turning the nut once specified torque is reached, as loosening a firmly fastened nut can cause media leakage.

Required Tightening Torques

Component Connection	Nominal Size (DN)	Tightening Torque
Solenoid fixing nut	DN 13...32	15 Nm
Solenoid fixing nut	DN 50	19 Nm
Valve cover screws	DN 13	3.0...4.0 Nm
Valve cover screws (325990)	DN 20	6.0...7.0 Nm
Valve cover screws	DN 25 / 32	8.0...10.0 Nm
Valve cover screws	DN 50	13.0...17.0 Nm
Stopper with armature tube	DN 13...32	49.0...51.0 Nm
Stopper with armature tube	DN 50	110.0...115.0 Nm
Cable plug center screw	Form A	Max. 1 Nm

Spare Parts and Accessories

Original replacement parts available for maintenance comprise:

• Item 1: Coil set
• Item 3: Armature wearing part set

When ordering replacement assemblies, specify the spare part item number alongside the valve article number 325990.

Compatible Cable Connectors

Cable plugs conforming to DIN EN 175301-803 Form A are available separately for electrical interface:

Accessory Type	Circuit Configuration	Voltage Range	Article Number
Type 2518	Without circuitry	0...250 V AC/DC	314802
Type 2518	With LED indicator	12...24 V AC/DC	314812
Type 2518	With LED and varistor	12...24 V AC/DC	314820
Type 2518	With rectifier, LED, and varistor	12...24 V AC/DC	314816
Type 2509	Standard Form A without wiring	0...250 V AC/DC	137943