If conventional pumps can no longer be used, e.g. injection of very small quantities (less than 1 l/h) or when pressure pulsation is unacceptable, Uhde's proportional injection units or so-called phase-flow intensifiers are the first choice.
Discharge
pressure range: 200 to 10 000 bar
Capacities: 0.1 l/h to 5,000 l/h
Capacity range: 0 ... 100 %

Uhde solved the problem by developing long-stroke hydraulically driven pressure intensifiers, using the experience accumulated in years of manufacturing high pressure equipment. Whilst certainly meeting the high demands of polyethylene producers, these pumps are also suitable for many other applications at low to ultrahigh pressure, e.g.

• Catalyst injection (0.1 to 2 l/h) into an LDPE tubular or autoclave reactor in pilot plants
• Pressure-controlled lube-oil and seal-oil injection into a stirrer-shaft bearing of an LDPE autoclave reactor
• Comonomer and/or modifier injection
• Special applications

A proportional injection unit (pump) has a side-by-side design, consisting of two HP intensifiers, each with a pump head including the necessary check valves, hydraulic cylinder, 4/2-way proportional control valve with integrated electronics, motion controller and pressure transducer. Electrically, both HP intensifiers are in an out-of-phase mode so that, during the discharge stroke of one pump head, the other goes through the suction and preload period. Electrical control and regulation are effected with the aid of motion controllers (position transducers) in combination with pressure transducers. Irrespective of the process data (pressure and medium compressibility), a smooth transition between the pump heads is thus obtained without the pressure drops normally associated with shifting the supply from one HP intensifier to the other. The unique design of the injection units allows the continuous pulsation-free injection of medium.

The piston velocity is controlled by regulating the hydraulic flow over the proportional valve via an external (remote) or internal (local) 4 - 20 mA control signal. Hence, the delivery rate of the injection unit is infinitely variable from zero to maximum. As an alternative, the units can be designed with pressure control.

• Robust design and rugged structural-steel frame
• Low hydraulic maintenance
• Slower stroking than most double-acting intensifers
• Simple interface to the customer's DCS hardware
• Fastest response to DCS signal
• Precise reproducible setting of the injection rate (< ± 0.5 %)
• Absolutely pulsation-free operation - superior pressure signal
• Best reliability and durability
• 30 years' experience with this kind of phase-flow intensifier

The described pumps are ideally suited for high pressure injection systems which must have absolutely pulsation-free operation and a perfectly reproducible and precise setting of the injection rate of the process pressure. In borderline cases or in special applications, do not hesitate to consult the Uhde specialists.