Eccentric disc technology originated in France, and was introduced to the market more than 100 years ago. In recent years the technology has become known worldwide and has moved from being considered "the best kept secret in the process pump industry" to being viewed as the most significant "new" pump technology of the decade.
Over the past decade, global competitive pressure and environmental protection regulations have forced companies to improve operating economics, pioneer new and sophisticated processing techniques and refine fluid transfer processes, pollution control and sanitary standards.
As a result, the demand for highly reliable pumps that can eliminate leaks, gently handle liquids and provide high-volume operating efficiencies and economic advantages has substantially increased.
Eccentric disc technology pumps can meet all these demands.
The key design benefits of eccentric disc technology include:
- Seal-less - there are no mechanical seals, magnets, rubber or teflon diaphragms.
- Self-adjusting - maintains delivery/pressure performance over time with automatic radial and axial disc/cylinder wear adjustment.
- Self priming and draining - and able to dry-run for up to 10 minutes. Capable of complete line stripping of suction and discharge lines of residual liquid.
- Clean-in-place (CIP) - can be completely drained, flushed and cleaned in place without disassembly.
- High volumetric efficiency - able to maintain a constant flow rate at a given viscosity throughout its pressure range.
- Low shear - gentle handling of product; low slip; lower internal velocities and ultra-low agitation.
The eccentric disc principle
Eccentric disc technology uses an oscillating eccentric disc to produce the pumping action and performance of a positive displacement pump, creating a constant flow that is independent of both pressure and viscosity. The oscillating motion of the disc within the cylinder causes very low internal velocity. The result:
- Gentle pumping action with very low slip (extremely low shear);
- No tip speed;
- Reduced internal parts wear;
- Lower energy consumption.
Performance characteristics
Eccentric disc pumps can be used as metering pumps because of their special radial and axial self-adjusting design features. Because the pump is automatically self-adjusting it maintains greater efficiency over time than traditional lobe or gear pumps.
The pumps have a shear rate of sec (-1) = 0.9 rpm; lower than circumferential piston, lobe and gear pumps. This is due in part to the gentle, oscillating action of the disc and cylinder and the low slip rate of the pump.
Unlike lobe and gear pumps, eccentrics do not have close clearances which can cause slip.
Slip is the portion of the pumped product that is forced back to the suction side of the pump due to pressure through the clearances.
The smallest clearance, for example on the Blackmer C-Series eccentric pump, is 0.157 cm. On these pumps, the discharge pressure exerts itself against the disc which prevents it from slipping. This low slip between the disc and cylinder allows the series to create high vacuum and compression.
Lobe and gear pumps have internal clearances, tip speeds and high internal velocities to contend with the fluid dynamics that can result in shear and slip. In lobe and gear pumps, as pressures and clearances increase and viscosities decrease, slip increases.
The C-series has a working pressure of 5-9 bar, depending on the model. The rpm speed range is 70-1000, with capacities of 1-588 L/min and an eccentricity range of 4.5-13.5 mm. Rated at 80°C, the series has a particle size range of 1-3 mm and can handle suspended solids with mild abrasives.
Construction
An eccentric disk pump consists of very few parts:
- A single drive shaft, machined on four (4) different planes;
- A single or double set of bellows that also act as a pressure retaining element;
- Four bearings that are separated from the liquid;
- One disc, made of acteon non-galling metal. A special metallic composition has been used in the construction (carbon 0.05, nickel 70, chrome 13, and molybdenum 3) to ensure high corrosion resistance;
- One cylinder;
- One gear case;
- One disc nut;
- Seven O-rings;
- Two lip seals.
Applications
From industrial applications to sanitary and food applications, eccentric disc technology is being used worldwide to solve everything from leak, suction, product shear and volumetric efficiency problems to offering unique benefits such as leak-free assurance, line stripping capabilities, metering and non-pulsating flow. Its eccentric principle makes the pump extremely flexible, capable of pumping low viscosity, high viscosity and abrasive materials within a single process, all with the same pump, demonstrating that output is not affected by viscosity variations.
Even at low speeds the suction capability of the pump allows for perfect priming and draining of mobile tanks and stationary pipes. Beyond the uniqueness of its eccentric disc pumping motion, its seal-less design makes it particularly suitable for a broad range of mediums, from sticky and highly viscous liquid sugars to toxic chemicals and extremely thin products such as solvents. Gentle handling, high volumetric capability and seal-less technology all wrapped into one.
