2-way cartridge valves, pressure functions LFT . DBW2 (high-pressure)

Description

• High-pressure series
• Size 25 … 50
• Component series 3X
• Maximum operating pressure 700 bar
• Maximum flow 3500 l/min

Features

• Stroke limitation (throttle function)
• Control cover with external pilot oil supply
• Control cover for set-up of directional and pressure valves

Product description

2-way cartridge valves are elements that have been designed for a compact block design. The cartridge valve type LCT is inserted into a special receiving hole in the control block and closed by a control cover type LFT. The control cover establishes the connection between the spring chamber of the cartridge valve and the pilot control valves. This enables implementation of pressure, directional and throttle functions – also in combination.

The main components of 2-way cartridge valves are the cartridge valve (8) and the control cover (2) with different functionality.

The cartridge valve (8) consists of a socket (3) with sealing package (4), control spool (5) and closing spring (6).

The control cover (2) seals the cartridge valve to the outside.

Besides simple control cover functions with external pilot oil supply, version "LFT . DBW2" is also suitable for complex switching functions thanks to its default directional valve connection surface. The connection surface is always closed pressure-tight (1). Suitable switching and proportional servo valves can be connected.

The relief pressure is set at the cartridge (7).

Due to structural-inherent requirements, some control cover versions feature high-pressure fittings leading to the outside. These are assigned a leakage bore L for indication of leakage at the HP fitting.

These ports are not suitable for external pilot oil supply.

Function

Passively controlled 2-way cartridge valves operate depending on the pressure ratio at working ports A and B. This results in three important pressurized surfaces for the function A1, A2, A3. The area at the valve seat A1 is defined as 100%. Depending on the version, the annulus area A2 realized by grading is 0%, 7% or 50% of area A1. The area A3 is identical to the sum of areas A1 + A2.

At pressure function, the area is A2 = 0. Respectively, the area is A3 = A1.

For check valve circuits, a 7% control spool with internal pressure feedback is available This way, the set-up of the block becomes less complex as external pressure feedback into the spring chamber via the pilot oil port X is not required (see "Circuit examples")

In general, the following applies:

The areas A1 and A2 are effective in opening direction. The area A3 and the spring are effective in closing direction. The direction of action of the resulting force from the opening and closing forces determines the working position of the 2-way cartridge valve.

Type code

Notices:

• On delivery, the control covers feature standard nozzle fitting (X, F, A). Nozzle specification in the type key is not necessary.

• Special operating conditions may require adjustment of the nozzle size. These must be specified in detail.

• All nozzles are designed as screw-type nozzles.

• For further information on nozzles, see "Accessories".

Standard nozzle fitting (Ø in 1/10 mm)

Technical data

general

hydraulic

(For applications outside these values, please consult us!)

Symbols/Circuit diagrams

NG25 … 32

NG40 … 50

Dimensions

Dimensions in mm

Dimensions in mm

Notices:

• The dimensions are nominal dimensions which are subject to tolerances.

• The leakage bore L of the HP fitting must not be closed.

• In case of leakage of hydraulic fluid at the leakage bore L, the HP fitting must be checked immediately. Further operation is not admissible.

• Remove eyelets (G) after transport or assembly/disassembly.

• By attachment of a pilot control valve, other valve functions can be realized.

Valve mounting screws (separate order)

Notices:

• The specified tightening torques stated are guidelines when using screws with the specified friction coefficients and when using a manual torque wrench (tolerance ± 10%).

• The specified tightening torques were calculated with total friction coefficient μtotal = 0.09 ... 0.14; adjust in case of modified surfaces.

Connection dimensions

Project planning information

• 2-way cartridge valves may only be assembled and commissioned by trained specialists.

• The special HP fittings are required for manufacturing reasons. Due to its special shape, their installation bore is not suitable for additional external connections. If necessary, please consult us.

• All control covers type LFT feature leakage indicators at the bottom as well as a special leakage bore L at the top of the cover. This enables simplified identification and diagnosis in case of leakage at one of the following components:
  – Pilot oil seal
  – Radial seal of cartridge valve type LCT
  – HP fitting

• Leakage bores L must not be closed. In case of leakage of hydraulic fluid, the HP fitting is defective.

• Eyelets for transport and assembly of control covers are installed by default as of NG40. It is recommended to remove the eyelets after assembly and reinsert them before disassembly.

• The essential valve components are coordinated with each other at the factory and marked accordingly. In case of faults, the complete valve assembly must be replaced.

• Use of the "depressurized circulation" function for decompression tasks is somewhat limited and should not be activated at maximum operating pressure.

• All control covers can be combined with directional and pressure cartridge valves. Pressure functions (particularly for pressure control) can only be implemented with version "LCT . DB".

• If nozzles are used, sufficient distance to downstream components must be ensured (jet erosion). Series control of nozzles (with staged pressure reduction) is preferred over single nozzles.

Information

Valve assembly components

Cartridge valve

The cartridge valves are hydraulically controlled via the two working ports A and B and via the spring chamber (supply via the control cover or internally via control spool bore). These assemblies are available in NG16 to 63.

All offered versions are fitted with shaft seals. This way, internal leakage between the spring chamber and port B is prevented.

Control cover

The control cover (2) can lead up to two pilot oil ports on the block side to internal components or additional externally mounted valve assemblies. Via the circuitry of the spring chamber of the cartridge valve (1), various circuit variations can be implemented.

All control covers have relief grooves at the bottom side. Failure of the internal seals is quickly and clearly indicated. On the top of the control cover, leakage at the HP fitting (4) can be identified at the leakage bore L (3) if applicable.

Pilot control valve (not included in the scope of delivery)

At control covers for set-up of a directional seat or pressure valve, the porting pattern is realized according to ISO 4401.

Multi-function cover "LFT_DBW"

By default, this cover is delivered with a connection surface for a pilot control valve. The connection surface is always closed with a pressure-tight blind plate.

By selection and assignment of the internal pilot oil channels, various switching functions can be implemented in addition to pressure functions.

Circuit examples

Check valve (RV1)	Check valve (RV2)	RV1 does not require an additional pilot oil bore X for spring chamber supply. At RV1, the Δp - q V characteristic curve is flatter.
Check valve (RV3)		RV3 permanently blocked in direction B → A Flow A → B can be blocked No internal leakage thanks to shaft sealing (standard) The locking pressure (channel P) can also be fed in externally.
Throttle valve (DV1)	Throttle valve (DV2)	DV1 and DV2 can be operated without spring for minimum cracking pressure; no closing force support. The spring chamber must be hydraulically connected (unloaded). At connection of the pressure supply on side "B", the mechanical load of the adjustment spindle is reduced if closed. In comparison to DV1, the mechanical load of the adjustment spindle at connection of the pressure supply on side "A" is higher at DV2. The adjustment should only be loosened (= opening the valve) at p = 0 bar or with pressurized spring chamber. The required torque of adjustment when closing the valve is defined by the applied operating pressure. For this reason, adjustment should only be regarded as additional mechanical protection. Ideally, the spring chamber should be supplied with operating pressure from the pressure supply while it is kept closed (see DV1).
Pressure limitation (DB1)	Pressure limitation (DB2)	DB1 with pressure-tight closed valve connection surface DB2 with proportional pressure adjustment and maximum pressure relief No internal leakage thanks to shaft sealing (standard)
Pressure limitation (DB3)	Pressure limitation (DB4)	DB3 and DB4 with set-up of a seat valve for "depressurized circulation" operating mode Frequent use of the pressure relief function ( p max = to T) increases the risk for cavitation erosion and early wear of the block installation bore At DB4, pressurisation of the pilot control valve is reduced by the 2/2-way pilot control valve if port A is closed on the cover side. The nozzle in port T reduces the effects of pressure surges in channel Y.
Combination function		Combination function with LCT directional application Keeps the cartridge valve closed even at p pilot < p A or p pilot < p B as long as a closing force is generated by the balance of forces acting on the control area of the control spool. For closing and keeping closed with p pilot, the surface and pressure ratios must be observed. No internal leakage thanks to shaft sealing by default By adjustment of the pressure relief valve to pmax, the function can be deactivated (if p pilot < p max)

Notices:

• When switching on/off the directional valve, observe the occurring pressure ratios in main port A.

• In case of application, relief of the spring chamber "F" while pmax is applied may lead to a pressure surge on the load side or abrupt pressure relief.

Accessories

Orifice selection

Orifices

HP plug screws

Ordering codes

Downloads

2-way cartridge valves, pressure and directional functions Data Sheet | RE21045 | 2021-08-01 | English, United States | PDF | 1.2MB Product Groups: 2-way cartridge valves Type LCT (cartridge valve); type LFT (control cover)