Chopper pump with double-edged cutting bars

An impeller assembly with an impeller and a cutter bar plate is used in a chopper pump system which handles liquid material sometimes entrained with large debris and stringy matter. The debris and matter present clogging hazards, which are reduced by a combination of scissoring between sharpened impeller blades and shearing fingers, and between cutting wings and shearing fingers. To make the cutting feature more aggressive, sharpened edges along two of the scissoring edges of the shearing fingers are utilized. Preferably, the sharpened edges are either the result of machined v-notches on the cutting surface of the shearing fingers or of a casted part having a cupped surface. Generally speaking, the impeller assembly comprises an impeller attached to a rotatable pump shaft and includes a back shroud.

TECHNICAL FIELD OF THE INVENTION

The present device relates to centrifugal pumps used for pumping liquids and slurries containing solid matter, including various types of refuse and debris. Specifically, the device relates to pumps having a cutter bar plate with the ability to reduce the size of such solid matter and prevent clogging on the upstream side of the chopper pump.

BACKGROUND OF THE INVENTION

Generally speaking, U.S. Pat. No. 3,155,046 to Vaughan, issued Nov. 3, 1964, discloses a centrifugal pump having a semi-open impeller with radial vanes. The vane edges adjacent to the pump inlet cooperate with sharpened leading edges of inlet apertures to cut stringy material or chunks entering the pump. Similarly, U.S. Pat. No. 3,973,866 to Vaughan, issued Aug. 10, 1976, and U.S. Pat. No. 4,842,479 to Dorsch, issued Jun. 27, 1989, disclose centrifugal pumps having impellers with vanes cooperating with inlet apertures to achieve a chopping or slicing action of solid material in a liquid or slurry being pumped. In the case of the pumps of U.S. Pat. No. 3,973,866 to Vaughan and U.S. Pat. No. 4,842,479 to Dorsch, however, semi-open impellers having shroud plates are used and external booster propellers may be provided to accelerate flow into the pump. The latter, when used, helps displace chunks of solid matter which become lodged in the inlet apertures and, at least in some instances cuts solid matter prior to entry into the pump.

One of the problems with each of these devices is the occurrence of motor overloading during heavy chopping. Where the chopping is not efficient, the motor power increases causing the motor protection controls to trip the motor offline. When the motor goes offline, the chopping stops and operator intervention is required to place the motor back online. The chopping down-time, of course, detracts from the cost effectiveness of the process.

Stringy material also presents a problem. The material becomes wrapped around the turning parts of the impeller assembly and can lead to plugging of the chopper pump inlet.

It is therefore desirable to provide an impeller assembly which helps maintain a clear cutting area, reduces cutting part wear and improves chopping efficiency to reduce motor power load and chopping down-time. It also would be desirable to provide an assembly which aggressively reduces the build-up and collection of stringy material, particularly around the external tool of the impeller assembly. The disclosed device affords other structural, manufacture and operating efficiencies not seen in prior art devices, as well.

SUMMARY OF THE INVENTION

There is disclosed herein an improved impeller assembly for a chopper pump. Generally speaking, the assembly comprises an impeller having a back shroud and cutting blades sharpened on a first edge, a cutter bar plate, and an external tool.

In a specific embodiment, the assembly comprises an impeller with cutting blades extending from and fixed on a first surface of the back shroud, and a cutter bar plate positioned adjacent to and upstream of the impeller, the cutter bar plate comprising at least one shearing finger having first and second contact surfaces and extending inward from a periphery, the first contact surface of the at least one shearing finger having a first sharpened edge such that the first sharpened edge creates a shearing operation in combination with the sharpened edge of the cutting blades of the impeller during use. Further, the embodiment includes an external tool positioned adjacent to and upstream of the cutter bar plate, the external tool comprising at least one cutting wing having a shearing surface that creates a shearing operation in combination with a second sharpened edge along the second contact surface of the shearing finger during use.

In other specific embodiments, the first sharpened edge has a length which is substantially equal to a length of the at least one shearing finger, while the second sharpened edge has a length which is substantially equal to a length of the at least one cutting wing. Accordingly, the second sharpened edge preferably has a length which is substantially less than the length of the first sharpened edge. Preferably, the first and second sharpened edges are both machined v-notches in the shearing finger and each is on a first cutting face of the at least one shearing finger. More preferably, the first and second sharpened edges are the result of casting of the shearing finger to create a cupped surface.

In specific embodiments, a gap between the at least one shearing finger and the cutting wing is in the range of from about 0.010 to 0.030 inches. Similarly, a gap between the at least one shearing finger and the sharpened edge of the cutting blades is in the range of from about 0.010 to 0.030 inches. Most preferably, the two gaps are in the range of from about 0.015 to about 0.025 inches.

A cutter bar plate for an impeller assembly in a chopper pump is also disclosed and claimed. A preferred cutter bar plate comprises a body configured to be positioned upstream from an impeller of a chopper pump, wherein the body comprises first and second opposing surfaces, the first surface being configured to face downstream and the second surface being configured to face upstream, and an opening defined through the body which allows material to flow past the first and second opposing surfaces, and at least one shearing finger fixed to the body and extending into the opening parallel to the first and second surfaces, wherein the at least one shearing finger comprises a front face normal to the first and second surfaces and having first and second contact surfaces. The shearing finger includes a first sharpened edge disposed on the first contact surface and a second sharpened edge disposed on the second contact surface.

In a specific embodiment, there are two shearing fingers and each comprises an aggressive curved-hook end.

These and other aspects of the invention may be understood more readily from the following description and the appended drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring toFIGS. 1-6, there is illustrated in the several views a chopper pump impeller assembly, generally designated by the numeral10, and various components of the assembly10. Generally speaking, the assembly10has a centrifugal impeller12, a cutter bar plate14, and an external tool16. The impeller assembly10is designed for use in a chopper pump system such as the one described in U.S. Pat. No. 7,125,221 and in U.S. Pat. No. 8,105,017, both assigned to Vaughan Company, Inc. of Montesano, Wash. The '221 and '017 patents are hereby incorporated by reference.

As shown in the embodiment ofFIG. 1, the impeller12has a series of radially extending blades20and a back shroud22to which the blades are attached. The illustrated impeller12is called a semi-open impeller due to the use of the back shroud22on one side. The impeller12connects to a motor and shaft (not shown) from the central hub24. As the impeller12turns, discharge pressure is created as material is pushed through the impeller12. Most of the material is liquid, suspended solid particle, and small debris. This material is easily discharged from the impeller chamber (i.e., the housing of the impeller) as a result of the fluid velocity created by the turning impeller12. However, large debris and stringy material can cause problems by blocking the inlet side and/or wrapping around the impeller12. As a means for helping reduce such problems, the upstream edges of the impeller blades20are sharpened for cutting action.

To assist the cutting action, the cutter bar plate14attaches to and is fixed at the inlet side of the impeller assembly10, as shown. A gap in the range of from about 0.005 inch (0.127 mm) to about 0.050 inches (1.27 mm) is maintained to create a scissoring between the impeller blades20and the cutter bar plate14. Preferably, the gap is in the range of from about 0.010 (0.254 mm) to about 0.030 inches (0.762 mm), and most preferably within the range of from about 0.015 (0.381 mm) to 0.025 inches (0.635 mm).

The cutter bar plate14is comprised of a planar ring-shaped body26having an upstream surface30and a downstream surface (not shown). The central region of the cutter bar plate14is open to allow material to pass through to the impeller12. However, at least one shearing finger32, and preferably two shearing fingers32extend into the opening. The shearing fingers32are preferably extensions of the inner surface33of the cutter bar plate14.

Each finger32has a front surface40and a backside surface42. At the end of each shearing finger32on the front surface is a curved hook44. This feature presents another cutting edge to help reduce clogging of the impeller by debris. The front surface40also includes a first contact surface (or junction)50where the front surface40meets the upstream surface30of the finger32, as well as a second contact surface (or junction)52where the front surface40meets the downstream surface of the finger32.

When the cutter bar plate14is positioned for use, the curved radial blades20scissor against the shearing fingers32as the impeller12turns. A first sharpened edge60along the second contact surface52of the shearing finger32helps in the reduction of clogging debris. The first sharpened edge60, as shown best inFIG. 3, is a v-notch machined into the finger surface52. Preferably, the sharpened edge60extends the entire length of the finger32and may even extend along the shared interior surface of the body26.

In addition to the cutting action of the impeller blades20and the shearing fingers32, an external tool16is positioned adjacent to and upstream of the cutter bar plate14. The tool16includes hex body70and cutting wings72, of which there are preferably two wings72. The external tool16is connected to the impeller12, so it also moves during operation. Like the gap between the shearing fingers32and the impeller blades20, the cutting wings72are similarly gapped from the shearing fingers32. That is, the gap is in a range of from about 0.005 inch (0.127 mm) to about 0.050 inches (1.27 mm) to create a scissoring between the cutting wings72and the shearing fingers32. Preferably, the gap is in the range of from about 0.010 (0.254 mm) to about 0.030 inches (0.762 mm), and most preferably within the range of from about 0.015 (0.381 mm) to 0.025 inches (0.635 mm).

A second sharpened edge62is shown as a v-notch machined into the first contact surface50of the shearing finger32. Where the edge62is a machined notch, as illustrated inFIGS. 1-3, the second sharpened edge62may have a shorter length than the first sharpened edge60to account for the fact that the cutting wings72do not extend the length of the shearing finger32. However, the use of longer cutting wings72on the external tool16would give rise to the use of a longer second sharpened edge62on the first contact surface50.

As previously mentioned, the first and second sharpened edges,60and62, are preferably machined v-notches made in the front surface40of the shearing finger32, as illustrated in the cross-section of finger32inFIG. 6a. The v-notch shape is believed to provide a sufficiently sharp edge for an aggressive cutting action. However, casting the shearing finger32(and the entire cutter bar plate14) is even more preferred. Casting would allow the sharpened edges,60and62, to be made by casting a shearing finger32having a cross section as shown inFIG. 6b. Like the v-notch, the “scallop” or cupped-shape also provides aggressive cutting edges on the front face of the shearing finger32. Other shapes and sharp cutting edge configuration might provide similar or even better results in different applications.

With reference toFIG. 4, an alternate embodiment of the cutter bar plate14is shown.

Two exemplary installations of chopper pump systems using the disclosed impeller assembly10are described below:

In 2015, four (4) model HE12W chopper pumps were installed at a Manatee County water treatment facility. Each pump comprised standard cutter bar plates having single notched shearing fingers. The pumps were brought online at a rate of about one unit per month over a period of a few months. Shortly thereafter, reports began coming in from Manatee County maintenance that all four pumps were experiencing periodic plugging at the pump suction side. Plugging would occur approximately once per month on each pump as debris would build-up over time on the pump suction side. As a result of the plugging, each pump would need to be shut down, unplugged, and then restarted on a monthly basis. This practice is both time consuming and costly.

In May 2016, all four model HE12W pumps were upgraded with double notch cutter bar plates. Over an eight (8) month period there have been no reports of clogging on any of the four pumps.

A chopper pump having a single notch cutter bar plate was installed at the City of Detroit. Each month the pump would show wrapping of material behind the external tool. A double notch cutter bar plate was installed in late 2016 and after two months has shown no sign of wrapping.