Prep high pressure PCP pumps

Liquid chromatography pumps - Prep high pressure PCP pumps

Pumps series PCP constitute the backbone of Labio production programme. PCP pumps use modular pumping heads and are manufactured as double- or quadruple-head pumps, using unified heads with three different piston diameters. At maximum output the pistons of these high-frequency pumps reach a frequency of up to 300 strokes per minute. All this imposes high requirements both on the quality of the transmission unit, which transforms the rotary motion of the motor into linear displacement of the piston, and on the material of the pistons themselves. The highest stress is always imposed on the seal. On the other hand, the high-frequency solution brings about a number of advantages, primarily low weight and low level of mobile phase pulsation.

The pumping heads are made of stainless steel quality AISI 316. The seats and balls of the ball valves are made of corundum ceramics. The valve inserts made from PEEK are held in inlet and outlet stainless-steel end pieces. Pistons are made from stainless steel covered with polycrystalline carbon, which bestows upon them diamond-like hardness and abrasion resistance. Multiple-part piston seals are made of high-molecular-weight polyethylene, PEEK and PTFE. The design of the pumping heads enables the piston behind the main seal to be flushed.

The pumping heads are attached to the transmission block by four holders, protrude from the front pump panel, and are easily removed (four screws). Tightening up the screws provides for the primary thrust of the sealing elements. Permanent thrust is provided by a set of springs situated behind the seal. The outlets from the pumping heads meet at the pressure-measuring gauge (mounted to the right of the pumping heads) with the outlet screwed fitting connecting the pump to the system proper.

The pistons of pumps series PCP are driven by circular cams with connecting bars held in ball bearings. Motion is transmitted to the pistons by means of piston rods consisting of planar steel profiles held in guide ball bearings. The steel profiles are pendulum-connected to the connecting bars and, on the other side, to the pistons.

In the laboratory version PCP L2 the cam shaft is driven by a quality dc motor with optoelectronic speed control within the range from 1:1 to 1:200, in the industrial two head pump PCP P2 and four head PCP P4 by an asynchronous motor of rating of up to 1,000 W via a multiple V-belt. The motor speed is controlled by a frequency converter, which enables the speed to be varied between 1:1 and 1:20.

Casing of the PCP pumps is made from a combination of a special, environmentally friendly plastic and stainless steel. The side panels are of fibreboard (MDF) containing a very small amount of organic polymers made from oil. The MDF fibreboard exhibits low ignitability, further reduced by surface treatment with an epoxide resin containing an inorganic filler (TiO2). The impregnation increases impact resistance as well. The side panels are then finished by application of a multilayer coating, resistant to standard chemicals and solvents.

The bottom and rear parts of the pump are made of standard stainless steel. The upper and front parts are pressed to shape from special, hardened stainless steel with openings for the display and the keyboard buttons. The latter are made of aluminium with a surface powder coating and symbols burnt by a laser technology. To prevent penetration of water and other liquids into the instrument each button has a rubber O-ring to seal the clearance between the panel and the button in its rest position.

An alphanumeric display and an eight-button keyboard are mounted in the upper, bevelled part of the front panel. The requested flowrate and the pressure limit can be set on the display together with the hysteresis of the pressure gauge. In gradient pumps the display also serves for gradient programming.

Gradient, electromagnetic valves mounted in the PCP pumps, with separate cores not flushed by the pumped liquid, represent brand new products of the firm ASCO. The valve core in its entirety is made of PEEK. The valves are supplied in sets of two or three units together with a stand and an outlet T-piece. Sets GVL2 or GVL3 are earmarked for laboratory pumps; the larger valves GVP 3 or GVP 3 are used in pumps earmarked for plant operation.