KRACHT KF U/U2 Gear Pump with Universal Valve

KRACHT KF U/U2 gear pump with universal valve for reversing drives

A normal gear pump moves oil from one port to the other, and when the shaft reverses the flow reverses too. The KRACHT KF U/U2 avoids this. Its universal valve is a small set of check elements built into the housing, so the suction and pressure connections stay on the same sides whichever way the shaft turns. The pump therefore keeps delivering to the same outlet in both directions. Seven Star LLC supplies KRACHT KF pumps in Oman and the GCC as an independent supplier in Muscat; this page covers the KF U/U2 universal valve versions.

There are two designs. The U valve fits nominal sizes 2.5 to 25 cm³/rev, and the newer U2 design fits sizes 32 to 112 cm³/rev. Rotation in the type key is B (sizes 32 to 112, U2) or U (sizes 2.5 to 25, U), both meaning right and left with a consistent discharge direction.

KF U/U2 technical specifications

How the KF U/U2 universal valve works

The valve housing sits between the gear set and the external connections. When the shaft reverses, the pressure side of the gear set changes, and the valve directs the delivery to the same external pressure connection as before and the suction to the same suction connection. The external piping never changes, and no separate reversing arrangement is required in the line.

KRACHT highlights one use in particular: guaranteeing lubrication of gearing in oscillating, or pendulum, operation, such as in wind turbine and marine propulsion gearboxes where the shaft speed and direction change with load and wave action. In those cases the pump turns with the gearbox shaft and must always supply the same lube circuit.

U versus U2 and sibling KF options

The U version for sizes 2.5 to 25 must be installed with its pressure piston lying horizontally, otherwise gravity affects the piston. The U2 version has no such restriction and may be fitted in any position, which simplifies layout on a gearbox. The U2 uses SAE flange connections on all of its sizes, whereas the U valve uses Whitworth threads. Compared with the KF D15/D25 relief valve and the KF T15/T25 tank-port valve, the universal valve is not a pressure-limiting device. It determines flow direction, and a separate relief valve should be fitted in the circuit to protect against overpressure.

The type key has a single valve position, and on these pumps it is taken by the universal valve, so a D-valve or T-valve is not part of the same code.

Selection checklist for KF U/U2

• Confirm that the shaft truly reverses; if it does not, a standard R or L pump without universal valve is lower in cost.
• Choose size 2.5 to 25 for the U valve or 32 to 112 for the U2 valve according to flow.
• For the U valve, make sure the installation allows a horizontal pressure piston.
• Check speed against the U2 limits: 3000 rpm for sizes 32 to 50 and 2200 rpm for 63 to 112.
• Specify the shaft seal; common choices are NBR, FKM or PTFE lip seals, and mechanical seals for demanding fluids.
• Provide for an external relief valve, since the universal valve does not limit pressure.
• State the mounting type: DIN flange, or mounting angle for the small sizes only.

Installation and maintenance of KF U/U2

Pipe suction and pressure lines to the connections on the valve housing and not to the pump body. The suction line should be short and straight with a full-bore strainer. The relative inlet pressure must remain above –0.35 bar for the U valve. When the shaft starts, the first revolutions must fill the valve elements, so prime the pump with fluid.

In oscillating duty the check elements switch many times per hour. Over time wear can show up as a loss of delivery in one direction. Record delivery pressure in each direction at commissioning so that the later comparison is meaningful. For a KF U/U2 in service, keep an eye on the shaft seal too, because reversing shafts transmit small shocks into the seal lip.

Applications of KF U/U2 in Oman and the GCC

Reversing lube pumps are relevant for marine propulsion on workboats and patrol craft in Omani waters, for geared drives that run in both directions on mixers, winches and test rigs, and for turbine barring gear or standby lubrication of rotating machines that coast down in either direction. Because wind turbines are growing in the region, pendulum lubrication is also relevant for gearbox spares. High oil temperature in the Gulf summer suggests FKM or PTFE seals and an oil viscosity grade checked at the hot end of the range.

Universal valve family table

Information to send with an RFQ for KF U/U2

• Nameplate type code or nominal size and design (U or U2).
• Application, for example gearbox lubrication in oscillating operation.
• Fluid, viscosity and temperature.
• Speed range and direction changes per hour.
• Connection size, mounting and shaft seal choice.
• Quantity and delivery site.

Documents and quotation

The manufacturer data sheet for the KF series, including the section on KF 2.5 to 112 with universal valve U and U2, is attached on this page and contains the type key and the dimensions.

Send the part number or duty data and we will confirm availability, lead time and a quotation for the KF U/U2 in Oman and the GCC.