Ebara ChopX chopper pump

The Ebara ChopX is EBARA HG's chopper pump, sold under the Hayward Gordon brand. It does two jobs in one casing: it reduces the solids and it moves the medium. That is the whole commercial argument for it. Where the alternative is a grinder or a comminutor in the line plus a pump behind it, you are buying one machine instead of two, with one set of wear parts and one thing to isolate.

EBARA HG puts it on scum pits, digester recirculation and digester scum blankets, on difficult lift station duties in prisons, hospitals and other public buildings, and on food waste, manure, fleshings, hides and bones. Pulp and paper gets wood yard sumps and chip and bark handling. The awkward list is the honest one: latex skins, plastics, paint sludges, detergent cakes and lagoon cleaning. These are the media where a conventional pump has already been tried.

There are two reasons to specify chopping rather than a bigger solids passage. The first is that the pump itself keeps blocking. The second, and the one that decides more jobs, is that something downstream cannot take the solids. Nozzles, heat exchangers and valves clog long before the pump does, and once the solids are reduced at the pump they stay reduced through the rest of the system. That is why EBARA HG builds its HydroMix digester mixing system around a ChopX and a set of nozzles in the tank rather than around a plain sludge pump.

Now what it costs you. Cutting takes power, so a chopper draws more for a given flow than a solids-handling pump doing the same duty, and the cutting faces are wear parts. They dull gradually rather than failing, which means throughput falls off before anything sounds different. Grit accelerates all of it. If the medium is abrasive, spend the money on the hard metal wet end and fix the grit removal upstream, because a hardened cutter bar in a gritty sump is still a consumable.

Check the flanges before you go any further. They are ANSI B16.1 Class 125, not PN16, so a UK installation needs the adaptation designed in rather than discovered on site. And be clear what you are buying. A ChopX is not the small-bore grinder pump set you would drop into a domestic or light commercial pressurised sewer. It is an engineered process pump built around a cutting head, and it is priced and sized accordingly.

If the pump on site is otherwise right for the duty and rag is the only problem, or if several pumps share one incoming flow, an inline macerator ahead of them usually does better than replacing each pump with a chopper. We will say so rather than sell you three ChopX units. Where the medium is fibrous but nothing downstream needs protecting, the Ebara XCS passes the material instead of cutting it, which is cheaper to run.

The ChopX uses an open-type impeller with sharpened leading and vane edges, and it cuts twice. The primary chop happens as the impeller's sharpened leading edges rotate in tight clearance across a cutter bar at the pump suction. A second cut happens behind the impeller, where sharpened vane edges on the rear of the impeller sweep across spiral grooves in the casing backplate. That second action cuts and expels stray solids from behind the impeller, which is what keeps them from binding the impeller or fouling the seal.

Chopper pump or macerator

A chopper pump cuts and pumps in one unit. An inline macerator only cuts, and sits in the pipeline ahead of a pump that is already correct for the duty. The ChopX is firmly on the chopper side of that line: EBARA HG's own argument for it is that it "provides cutting and pumping action in a single unit", saving the capital and maintenance cost of a separate grinder or comminutor. Choose the chopper when the pump and the cutting are one purchase; choose the macerator when the pump stays and only the rag has to go.

The cutter bar and the clearance

The cutter bar sits in a replaceable, externally adjustable suction plate. Its face towards the impeller carries multiple radial cutting slots, which stop material binding between the plate and the impeller vanes. On pumps with impellers of 381 mm (15 in) diameter and above, the cutter bars are separately replaceable from the main suction cover, so you renew the cutting faces without the whole plate.

Clearance between impeller and cutter bar is the number that decides whether the pump still cuts. EBARA HG's specification sets it at 0.25–0.38 mm (0.010–0.015 in) on impellers below 356 mm (14 in) diameter, and 0.51–0.76 mm (0.020–0.030 in) at 356 mm and above. Axial clearance at the front and rear of the impeller is externally adjustable, taken up on the double row thrust bearings in their own housing. Set the exact figure for your model from Hayward Gordon's manual at overhaul, and read the designation and serial number off the nameplate before you order anything.

A deflector nut holds the impeller on the shaft. It is 420 stainless hardened to 400 BHN, and it is shaped to protrude in front of the cutter bars so stringy material is deflected rather than allowed to wrap the shaft. For solids too large to enter the suction cleanly, an optional disintegrator tool at the inlet breaks them up first.

Materials

The standard casing is ASTM A48 cast iron with ANSI B16.1 Class 125 flanged suction and discharge. Impeller and cutter bar are cast alloy steel case hardened to a minimum of Rockwell C 60, which is what does the cutting. Where the medium is abrasive or corrosive, the wet end can be taken to ASTM A532 high chrome iron at 450 BHN minimum, Ni-Hard, hardened alloy steel, 316 stainless or CD4MCu. Clamp type construction with integrally cast feet is what makes hard metal practical, because it removes the drilled and tapped holes those metals do not tolerate.

Casings with a 4 in discharge or larger carry an inspection port with a removable cover, and there is a second port in the suction spool piece giving access to the front of the impeller and the cutter bars. That matters more than it sounds. On a chopper the first diagnostic is a look at the cutting faces, and a port means you do it without breaking into the pipework.

Sealing, including the flushless option

Three sealing arrangements are catalogued, and only one of them runs without a clean water supply.

On a sludge, scum or digester duty the flushless cartridge is usually the one to specify.

The flushless system works by shape rather than by water. The stuffing box portion of the seal housing opens out at no less than 20°, which pushes solids back into the pumped flow instead of letting them pack in front of the faces, and the impeller back shroud is left open so pumpage circulates freely around the seal. The seal itself is a front-loading cartridge with silicon carbide faces, Viton O-rings and 316 stainless metal parts, pre-assembled and pre-tested so nothing is set in the field, with the springs shielded from the pumped medium so they cannot hang up. No separate oil chamber is needed. Where dry running is a real possibility, an oil quench is available.

What you gain is no dilution of the process and no flush piping, valves or gauges to install and maintain. On a digester that dilution is not a trivial point, since seal water added at the pump has to be handled by everything downstream of it.

Configurations

The ChopX comes in horizontal dry pit, vertical dry pit, close coupled, submersible, immersible and vertical bearing builds. The horizontal pumps use a back pullout powerframe with a clamped wet end, driven direct or on V-belts, with shafts and bearings sized for a minimum 100,000 hour L10 life. Radial bearings are cylindrical roller on every size, because a chopper takes heavy radial load while it cuts. Thrust is taken by double row angular contact bearings below a 356 mm impeller and by double row tapered roller bearings at 356 mm and above.

The vertical sump build is for sumps to 7.6 m (25 ft). Its shaft is supported along its whole length by anti-friction bearings running in an oil bath formed by the pump column, with a protection system that shuts the pump down if the oil level drops, and the lower shaft section has its own independent powerframe so shaft deflection at the seal does not grow with pump length. Its seal is hard faced, set screw driven, with no exposed springs and self-aligning faces.

The close coupled build takes a standard JM or JP frame motor on a spigotted back pullout assembly. There is no coupling to align, no bearing frame to maintain and no field alignment. Close coupled sizes run from the CHOPX3, with a 6 in suction and a 3 in discharge, to the CHOPX8L at 8 in on both. The powerframe is fully interchangeable with the XCS Series, which is worth knowing if you run both ranges on one works, because it cuts what you hold on the shelf.

Recirculation and mixing

A diverter valve and recirculation nozzle assembly can be fitted to the discharge of the submersible and vertical wet pit builds. It lets you mix a pit or a tank before pumping it out, and inside a digester it breaks up the scum blanket. The nozzle adjusts a minimum of 180° horizontally and 70° vertically, on control rods operated from outside the tank, and the valve gives full, partial or no recirculation. The valve body is ASTM A48 Class 30 cast iron with a 316 stainless disc on a Graphalloy bushing. An electric ball screw linear actuator is available to position it, and controls can include level control, duplex pump control and variable speed drives, with alarms for high temperature, low oil, seal leakage and level.

Motor and hazardous areas

The submersible motor is air-filled with copper windings, NEMA Design B, Class F insulation minimum rated at 155°C, with two normally closed automatic reset thermostats in series in adjoining stator phases. It is rated for continuous full load duty fully submerged with no external cooling, and EBARA HG rules out a cooling jacket as an equivalent. Nameplate ratings are based on a 40°C ambient, the seals are designed for 200 psi differential water pressure, and the motor is rated to run 15 minutes in air. Allow 15 starts an hour, a service factor of 1.15 minimum, and a 10:1 turndown on an inverter at unity service factor.

On hazardous areas, read the wording as it stands. EBARA HG's specification calls for an explosion proof TENV-TEXP motor construction capable of being certified for Class I, Groups C and D hazardous locations by Factory Mutual or Underwriters Laboratories. That is the North American scheme. A classified area in the UK is classified by zone, and the equipment carries an ATEX category under Directive 2014/34/EU, which is a separate certification. Tell us the zone and we will establish what can be certified for it before anything is quoted.