A "Green" Company Since 1990

API Series Oil/Water Separators

Follow this link for information on HydroFlo's

"Oil Water Separator Design Parameters"

for information on the accurate design and sizing of
Oil Water Separators and Separation Systems

The HydroFlo Tech API oil water separators are the performance, safety and environmental standard by which all others are judged. Our separators are installed at some of the largest chemical and petroleum refineries located throughout the world.

Our API separators are designed to the highest standards available today, guaranteeing a risk-assessed, safe operation. Above ground, steel fabrication provides double-containment and visual leak detection for hazardous sludges and wastewater. VOCs are contained through the use of vapor-tight covers. Additional safety features include non-metallic collector components and covers, stainless steel on all wearing metallic components, deflagration vents, flame arrestors, and more.

Sludge collection hoppers, screw conveyors, flushing connections, clean-outs, sludge withdrawal piping, and sludge pumps are designed to remove and transfer API separator bottoms with minimal maintenance and operator attention. Sludge handling and effective removal is critical. The inability to remove thick, sticky sludge is the main reason for separator failures in severe duty applications.

Standard Features:

  • Adjustable effluent weir troughs

  • Epoxy coated ASTM A-36 carbon steel tank
  • Factory tested
  • Seamlessly integrates with other HydroFlo offered wastewater products
  • Stand alone operation
  • Standard units can be manufactured for flows from 5 gpm to 3000 gpm and above, in a single above grade tank
  • Structural steel support legs

Available Options:

  • Access platforms with ladder or stairs

  • Automatic sludge pump out packages
  • Chemical pretreatment systems
  • Concrete tank designs for large in ground installations
  • Duplex systems for redundancy
  • Effluent monitoring
  • Effluent sampling
  • Explosion-proof design
  • Flash mix/flocculation tanks with mixers
  • Full FRP or stainless steel construction
  • Influent equalization
  • Influent / effluent lift stations
  • Instrumentation and controls
  • Removable covers with gaskets
  • Integral mechanical sludge thickener
  • On board reagent storage (day tanks)
  • Pilot size units for on-site testing
  • Potable water design
  • SCADA system monitoring
  • Special coatings
  • Sludge handling and dewatering


Equipment Design Data & Sizing Calculations

Oil Water Separator
Theory of Operation

Oil Water Separator
  Design Parameters

Oil Water Separator
Test for Determination of

  Susceptibility of Separation

API Oil/Water Separator
  Sizing Spreadsheet

Application Questionnaire


General Arrangement


• Standard Engineering

"Common" Engineering
  Applicable to all HydroFlo
  Manufactured Equipment

Installation, Operation & Maintenance Manuals

Standard IO&M Manual

General IO&M
  Applicable to all HydroFlo
  Manufactured Equipment

Equipment Criteria:

The separator shall be a specially fabricated rectangular channel tank. The separation process shall be fully automatic requiring no moving parts. The design of the separator shall satisfy the requirements of API PUBLICATION 421, Feb. 1990 on DESIGN & OPERATION OF OIL/WATER SEPARATORS and Stokes' law.

Separation Cell:

The separation cell is designed using elements of American Petroleum Institute's publication 421, Feb. 1990, “Design of Oil-Water Separators” to ensure the best possible use of particle rise rate performance. The separation cell is a rectangular “V” bottom tank manufactured from carbon steel with an effluent surface baffle, 304 stainless steel, full width, adjustable overflow weir, effluent collection chamber with flanged outlet nozzle and recycle suction port, and angled float beaching plate.

  1. Influent Diffusion Chamber
    The flow shall enter the separator submerged, through an influent diffusion chamber. Dispersion across the depth and width of the DYNA-PAK is to be achieved through the use of a non-clog diffuser. Heavy solids that fall out of suspension here shall be channeled to the sludge collection chamber.
  2. Separation Chamber
    The Separation Chamber shall be fitted with DYNA-PAK cross corrugated coalescing media. Adequate space will be left before and after the chamber to prevent short circuiting through the pack. A total of ____ cubic feet of coalescing media is provided with ½, ¾, or 1-1/4” spacing providing _______ft3 of coalescing surface area.
  3. Sludge Collection Chamber
    The sludge collection chamber shall be located directly beneath the coalescing media pack and provide ample storage capacity for the settled sludge. The sides of the chamber shall be sloped at 45 degrees to insure easy and complete removal of the settled sludge.
  4. Oil Trough
    The oil trough shall be located at the influent end of the separation chamber and incorporate an angled float/oil skimming plate.
  5. Effluent Chamber
    The aqueous phase leaving the DYNA-PAK shall pass under the oil retention baffle and up over the adjustable 304 stainless steel effluent weir, which shall maintain the liquid level throughout the separator.
  6. Removable Lids
    The entire separator shall be covered with bolt down removable lid

Surface Skimmer (Optional):

Provide a removable float skimming system with frame assembly and drive motor, sprockets, chains and full width stainless steel skimming blades. The skimmer blades are mounted on swivel pins that are fastened to the skimmer chains and maintain the blades in a down position at all times. The conveyer chains are provided with drive sprockets on a full width shaft at the drive end and four independent idler sprockets at the return end. The skimmer system frame shall provide a sprocket tension adjustment device and the carrying and return tracks for the chain. The entire system shall be self supporting with side and end channels, and cross members with lifting lugs that permit removal of the skimmer assembly as a complete unit for easy cleaning and service. The skimmer drive system is provided with a hollow shaft gear reducer that is maintenance free.

Bottom Sludge Auger (Optional):

The ribbon flight auger is made from 304 stainless steel, has converging flights to gently move settled sludge toward the sludge outlet nozzle and is driven at 3-5 RPM by an industrial duty TEFC motor with gear box speed reduction.

Operational Criteria
Overflow ratio of _____ GPM/ft2 settling surface area at a flow rate of ___ GPM.
Maximum allowable wastewater temperature = 1308 F

Control Package (Optional):

All HydroFlo Tech oil/water separation systems are fully automated. Control packages (depending on your specific requirements) are available in either basic relay logic controls, or a full state of the art PLC with touch screen HMI and our sophisticated treatment algorithms. The relay logic controls package allows basic reconfiguration of the original system settings, while the PLC based package allows maximum flexibility to change the process parameters, as well as tight control that minimizes chemical usage. We can include a variety of options including digital data logging of critical process parameters, ethernet access to process data, communication with Building Management Systems, and even remote system access using cellular wireless technology.

All enclosures are NEMA 4X. Where metallic enclosures are used, they are provided with epoxy or polyester finishes for corrosion resistance. All conduit is plastic coated where possible. Low voltage 24VDC is used throughout to minimize service personnel exposure to high voltage. All panels are OSHA LOTO and NFPA 79 compliant. Additionally UL-508 listing is available.

Effluent Monitoring: As mandated by the local controlling authority, the effluent quality must be continuously monitored. A two pen recorder is to be used to monitor effluent flow rate and pH. The recorder is to be equipped with a flow totalizer. Any effluent pH deviations will trigger an alarm and system discharge will be halted.

System Packaging:

The system is supplied as a completely fabricated "turnkey" package. All devices are pre-wired and plumbed.

You need to make the plumbing connections to and from the system and a single electrical connection point for incoming power. The disconnect on the MCP provides OSHA Lock Out / Tag Out and NFPA 79 compliance. For systems requiring compressed air, only one connection is required and the valve is supplied for OSHA LOTO.