The Progressing Cavity (PC) Pump excellent for handling abrasive sludges, slurries, and metering applications at Waste Water Treatment Plants. It also offers the following additional Benefits:
- Ability to handle thick fluids (Polymer in excess of 1,000,000 centipoise/70 solids cake from plate and frame filterpress)
- Ability to meter accurately (controlled flow rate for feeding dewatering equipment)
- Ability to handle solids without damage (will not harm floc)
- Ability to handle shear-sensitive fluids without agitation (will not damage polymer)
- Suction lifting and self-priming (can suction lift H20 up to 28 feet)
- Ability to maintain constant flow rate with wide variations in suction and discharge head conditions (flow rate will be the same whether tank is at high level or low level or regardless of sludge being thick or thin)
- Non-pulsating flow
- Energy-efficient
- Low noise level
- Maintenance and repair capable of being done on-site by the treatment plant’s staff
Sludge Pumps for Waste Water Treatment Plants
First, consider the abrasive characteristics of the sludge. For purposes of selecting progressing cavity pumps, most municipal sludges are considered to be of medium abrasion. Some municipal sludges are considered to be of heavy abrasion. The following are common causes of sludge of heavy abrasion:
- combined storm and sanitary sewers
- ineffective or no grit system
- rocks
- snails
- trash (tramp metal, bottle caps, sticks, wire, glass, etc.)
Progressing cavity pump selection is different for sludge of medium abrasion than it is for sludge of heavy abrasion:
| Medium Abrasion | Heavy Abrasion | ||
| casing material: | cast iron | casing material: | cast iron |
| rotor material: | tool steel, chromeplated | rotor material: | tool steel, K-37 ceramic coating, oversize |
| stator material: | nitrile/Buna N rubber, 70 durometer | stator material: | nitrile/Buna N rubber, 55 durometer |
| shaft material: | tool steel, chromeplated on stuffing box area;consider shaft sleeve | shaft material: | tool steel with shaft sleeve |
| sealing: | packing (grease lubricated) or mechanical seal; consider water flush system | sealing: | packing with water flush system |
| max. pressure per pump stage: | 35 psi | max. pressure per pump stage: | 15 psi |
| max. pump RPM: | 300 | max. pump RPM: | 200 |
General Specifications for Sludge
specify crown gear-type universal joints
specify inspection ports/clean-our ports/handholes
specify hollow shaft
if sludge has more then 10 percent solids, specify open throat, hopper-type suction port
specify pressure relief system (pressure sensor/switch, rupture disc. pressure relief valve) on discharge side of pump
if there is a chance that the pump could accidentally run dry, specify a flow detection device on suction side of pump
Special Condition Pumping Sludge with a PC Pump
high rag/hair/stringy material content
- consider sludge grinding
- if there is no sludge grinding, specify protective cover on universal joint-shaft
area
NOTE: Inspection ports/clean-out parts/handholes and hollow shaft are strongly recommended when sludge has high content of rags, hair, or stringy material.
high rock or trash (tramp metal, bottle caps, sticks, wire, glass, etc.) content
- consider sludge grinding
- specify a trap (inverted tee) in the suction line
Suction lifting/long suction lines/negative suction conditions
- If packing is used as the sealing device and the discharge pressure is less than 50 psi, specify the pump to operate in reverse rotation (this puts the stuffing box on the pressure side of the pump, eliminating the possibility of pulling air through the packing), or utilize a mechanical seal as the sealing device or specify a water seal system for the packing (this is not as fail-safe as reverse rotation)
COMMON APPLICATIONS FOR PROCESSING CAVITY PUMPS IN THE WASTEWATER TREATMENT INDUSTRY
Progressing cavity pumps are commonly used in the following wastewater treatment applications.
Sludge Pumping applications
- primary
- secondary
- thickened
- waste-activated
- digested
- OAF
- mixed liquor
- feeding dewatering equipment
- belt presses
- centrifuges
- vacuum filters
- plate and frame filterpresses
- feeding incinerators
- feeding heat exchangers
Chemicals-metering/dosing & transfer
- polymer
- lime slurry
- ferric chloride
- alum
- others
Scum & grease
Raw sewage
- high head lift stations
- sampling
Dewatered sludge (cake)
- from belt presses
- from centrifuges
- from vacuum filters
- from plate and frame filter press