Gravity Sand Filter
Side Bar Filter PressHoffland Environmental’s low profile gravity flow sand filter continuously filters, by gravity, liquid suspensions producing excellent filtrate while simultaneously and continuously cleaning the filtration bed.
HEI’s low profile filter backwashing is a unique process. A slip stream of the most contaminated media, is taken from the bottom, cleaned and automatically redeposited on the top of the filter bed. The filter bed media slowly moves downward as the filtered water moves upward through the bed.
Since the HEI gravity flow sand filter continuously cleans a small portion of the media bed, the dirty backwash water, comprising approximately 5% of the total flow, may be continuously returned to the primary clarification device without stopping or surging the system.
A conventional pressure sand filter backflushes on a batch basis producing large intermittent flows of wastewater. In addition, the large volume of backflush water must be accumulated and held in reserve until it can slowly be treated. The HEI low profile continuous backflush sand filter eliminates the requirement of tanks and pumps to store, pump and process the backflush water.
HEI gravity flow sand filter is a low profile designed unit enabling direct flow of the influent from standard clarifiers. A conventional clarifier does not need to be raised to provide the required water column for HEI’s sand filter operation. And, as well, pumping or lift station from standard clarifiers are not required with HEI’s low profile media filter.

Advantages of HEI’s Low Profile Media Filter

Low Profile Gravity Sand Filter VS. Pressure Sand Filter
Filtration Equipment Required:
1. One (1) HEI Gravity Sand Filter

Filtration Equipment Required:
  1. Influent Surge Tank
  2. Influent Pressurization Pump
  3. High Pressure Vessel
  4. Pressure Sand Filter
  5. Backflush Pump
  6. Backflush Reservoir
  7. Waste Backflush Surge Reservoir
  8. Waste Backflush Return Pump
  9. Pressure Sand Filter Controls
    1. Pressure Switch
    2. Pressure Guage
    3. Air Vent
    4. Compressed Air Media Scrubber
    5. Pressure Relief Valve
    6. Automatic Valves With Operators
    7. Valve Positioners
    8. Valve Position Indicators
  10. Central Control System
    1. Motor Starters
    2. Disconnect
    3. PLC
    4. Switches
Continuous filtration with only a small continuous flow of backflush wastewater creates problem free performance. HEI’s trouble free units provide the following advantages:
  • Eliminates equipment and tankage to store large volume of backwash water.
  • With a small slip stream of backflush water, the wastewater treatment system does not need to be increased in size to accommodate large intermittent flows backflush water.
  • Eliminates the pumps required for backflush.
  • Eliminates electronic controls, PLC’s, motor starters, pressure switches, level controls required to control the filter and and process the backflush waste water.

Uncomplicated Design

Full automatic operation is achieved without operator assistance. The filter media is continuously backwashed at a rate controlled by simply adjusting the air supply to the air lift mechanism. This eliminates the batch operation common to pressure media filters backwashing. Since there are no moving parts or pumps required in the HEI gravity sand filter, the required operator attention is minimal.
Low Profile Design
The maximum height of the HEI gravity sand filter is only nine (9) feet, gravity flow from a conventional clarifier is readily achieved. Elevating the clarifier, recessing the sand filter or additional pump stations are not required.
The HEI gravity flow sand filter continuously cleans a slip stream of the contaminated media and redeposits the clean media on the filter bed. The filtrate continuously flows through clean media.
Efficient Design
With the internal media backwashing design, capital cost of all external backwashing equipment including backwash influent storage tank, backwash effluent storage tank, high volume backwash pumps, and all related controls, is not required. The floor space required is limited to only the HEI low profile sand filter vessel. The overall cost of HEI’s self cleaning gravity flow media filter is significantly less than a pressure sand filter system, when all tanks pumps, controls etc. are considered.
Simple Installation
HEI’s gravity flow media filter is shipped completely pre-assembled. Only influent, effluent piping, and air supply are required.
Complete Range of Sizes
The HEI sand filter is manufactured in standard sizes varying from 10 sq. ft. (50 gpm) to 150 (750 gpm) sq. ft. of surface area in one unitized package. Multiple units may be manifolded together for larger flow rates.

HEI Low Profile Gravity Sand Filter

"The Proven Concept in Sand Filtration"
The HEI Sand Filter is a continuous backwash, upflow, deep-bed granular media filter. The filter media is continuously cleaned by recycling the sand internally through an airlift pipe and sand washer. The regenerated sand is redistributed on top of the sand bed, allowing for a continuous uninterrupted flow of filtrate and reject (backwash) water.
Feed is introduced into the bottom of the filter, then flows upward through the inlet tube (H) and is evenly distributed into the sand bed through the open bottom of an inlet distribution hood (A). The influent flows upward, through the downward moving sand bed (B), with the solids being removed. The clean filtrate exits from the sand bed, overflows a weir (C), and is discharged from the filter (D). Simultaneously, the sand bed, along with the accumulated solids, is drawn downward into the suction of an airlift pipe which is positioned in the center of the filter. A small volume of compressed air is introduced into the bottom of the airlift (E). The air lifts the dirty sand up the airlift pipe, and air scours the sand at a rate of 100 to 150 SCFM/ft.2. The impurities are scoured loose from the sand during this violently turbulent upward flow. Upon reaching the top of the airlift (F), the dirty slurry spills over into the central reject compartment. The splash hood (Q) protects water coming over to the effluent weir (C). The sand is returned to the sand bed through the gravity washer/separator (G) which allows the fast settling sand to penetrate, but not the dirty liquid. The washer/separator is placed concentrically around the upper part of the air-lift and consists of several stages to prevent short circuiting. By setting the reject weir (J) below the filtrate weir (C), a steady stream flows upward, counter-current to the sand, through the washer section, over the sand distribution cone (P) and cleans the sand at a backwash loading rate of 50-100 gpm/ft.2. A continuous reject flow exits near the top of the filter (K), carrying away the dirt and impurities removed in the filter. Since the sand has a higher settling velocity than the dirt particles, it is not carried out of the filter. The clean sand is then redistributed after exiting the bottom of the gravity washer/separator. The sand bed is continuously cleaned while both a continuous filtrate and a continuous reject stream are produced.

Key Feature

The HGSF sand filter line was originally designed with the customer in mind. Hoffland Environmental, Inc. has overcome the height problem that all of its competitors have. By using its revolutionary patent pending inverse cone design, HEI can literally save the customer money by decreasing the height of the system.
Get it right and for less the first time with the HGSF line from Hoffland Environmental, Inc.
No need for clarifier stands to gain height for gravity flow.
No need for expensive lift stations.
Filtration Area (ft2)
Sandfilter O.D.
Tank Height
84 1/2"
96 1/2"
108 1/2"
108 1/2"
108 1/2"
108 1/2"
108 1/2"
Feed Rate
50 gpm
100 gpm
200 gpm
300 gpm
400 gpm
500 gpm
750 gpm
Air Consumption
2 cfm
2 cfm
6 cfm
6 cfm
8 cfm
10 cfm
12 cfm
Sand (cuft)
32 cuft
55 cuft
144 cuft
214 cuft
296 cuft
340 cuft
460 cuft
Sand Bed Depth
Sand Lifts
Pressure Drop
15"- 20"
18"- 24"
18"- 24"
18"- 24"
18"- 24"
18"- 24"
18"- 24"


  • Wastewater Treatment
  • Metal Hydroxide Removal
  • Process Water
  • Cooling Towers
  • Water Reuse
Ground & Surface
  • Remediation
  • Algae Filtration
  • Well Water
  • River & Pond
  • Water Reuse
  • Phosphorus Removal
  • Tertiary Filtration
Other Products by HEI
  • Inclined Plate Clarifier
  • Membrane Filtration / Reverse Osmosis
  • Filter Press
  • Polymixer
  • Dissolved Air Flotation
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