Uhde is one of the leading high pressure pump suppliers for low-density polyethylene plants. Since 1935, more than 1,000 HP pumps have been installed worldwide.
Typical applications for Uhde HP pumps in the pressure range of 125 - 14,000 bar and with discharge capacities of 10 - 20,000 l/h are:

• Injection
• Proportioning
• Testing
• Pressurising
• Product feed

Reciprocating pumps, or so-called double-acting oscillating pumps, for the high pressure LDPE market have been developed and manufactured since 1954. Approx. 600 HP pumps have been delivered for catalyst injection in autoclave and tubular reactors and for all known licensors.

Typical pump services in a low-density polyethylene plant are:

Discharge
pressures: 1,500 to 4,000 bar
Capacities: 10 to 140 l/hr

Discharge
pressures: 250 to 365 bar
Capacities: 600 to 3,000 l/hr

Discharge
pressures: 4,000 to 14,000 bar
Capacities: 20 to 100 l/hr

These units can be foundation-mounted or supplied in a trailer-mounted design which means that they can be used anywhere in the plant.

The pumps are hydraulic pressure intensifiers with an oil-hydraulic drive, built up from standard component parts/modules. They are available in a 2-plunger or 4-plunger design. Pressure-relief valves in the hydraulic system protect both the hydraulic components and the components wetted by the high pressure process. The discharge rate of the pump is infinitely variable from zero to maximum during standstill and also while the pump is in operation by simply changing the stroke frequency. Additionally, the discharge rate may be varied during standstill by changing the stroke length. The patented control system (DBP 2011570) develops extremely short plunger reversal times, thus guaranteeing a superior pressure amplitude and exact feed-rate control, and leads (e.g. in the case of catalyst injection) to a very good reactor temperature stability of up to ± 0.1°C. 4-plunger pumps consist of two separate HP units operated individually by one single hydraulic drive. One unit is in operation and the other in a stand-by mode. If the stand-by unit is to be put into operation, it can be brought up to the operating pressure by a prepressurising system. Thus, the second unit can be started immediately without influencing the reactor temperature. The so-called Uhde HP-4-Plunger "twin pump" consist of two independent HP-2-Plunger pumps, each with an oil-hydraulic drive mounted on a common frame. With this system, it is possible to pump two different fluids at different pressures and capacities. This model is chosen, for example, if the set-up space is limited.

Constant research and development and the exchange of experience with our customers leads to excellent service lives of the main components in catalyst injection pumps. Uhde's unique combination of duplex pump-body design with a tungsten-carbide liner, a solid tungsten-carbide plunger, a floating plunger coupling and the dynamic packing itself maximises the packing life to as much as 16,000 hours. The pump body (HP cylinder) even reaches a service life of 7 to 10 years and ultralight double-ball check valves 1 to 2 years. All pressure-containing parts are autofrettaged at optimum pressures.