Candle Filters

Classical Tubular Filters

The Auto-Shok and Auto-Pulse Filters are classical tubular filters, also known as Candle Filters

Auto-Shok Tubular Backpulse Filter

Veolia’s Auto-Shok is a candle style filter. The vertical vessel is equipped with a tube sheet located in the upper side shell. The tube elements are fastened to the tube sheet so that the liquid is filtered from the outside, through the openings in tube sheets and inside into the top head above the tube sheet. The top head has a compressed air volume above the filtered liquid that is quickly released to generate high-flow energy for back flushing of the tube elements and removal of the cake.


Veolia’s Auto-Shok tubular filters reduce capital costs and ease installation efforts because of the following advantages of its design:

  • Self-contained internal backwash liquid source. There is no need for auxiliary equipment such as external backwash pumps or tanks.
  • Rapid cleaning cycles. With minimum downtime, the need for additional filters is eliminated.
  • Removable tubular bundled assembly which can be easily replaced and/or maintained as a single unit.
  • Small footprint that minimizes installation costs and facilitates installation around existing infrastructure.
  • Engineered tube design with perforations along its entire length to reduce pressure drop during filtration and ensure optimal distribution of the backwash energy during cleaning. 


The start of the cleaning sequence is triggered as the pressure drop across the tube elements reaches a predetermined setpoint during filtration. Next, the service cycle is stopped and the inlet and outlet are closed. The filter is then pressurized from an external pressure source (e.g. feed pump) and compressed air is applied to the top dome. Once an internal pressure of 60 psi has been reached, the drain valve is quickly opened to allow the filtered liquid to backwash the tubes.


Designed in standard sizes from 40 to 450 sq.ft. of filtration area, this filter has been used for many applications from brine filtration to condensate polishing and beyond into any high flow rate, low-solids liquid influent. Large amount of surface area in a vertical vessel offer wide flexibility in precoat filter aid materials including diatomaceous earth, cellulose, powdered ion exchange resin and more.

Because Auto-Shok has minimal metallic parts and its components can be rubber lined, Auto-Shok is the technology of choice in the Chlor-Alkali industry due to its superb capacity to deliver excellent filtrate quality in corrosive environments with exposure to brine. When precoated with powdered ion-exchange resin as a filter aid material, AutoShok is also used in condensate applications in the power and petrochemical industry.

Auto-Pulse™ Bump & Run Tubular Backpulse Filter

Auto-Pulse is a tubular backpulse filter designed to achieve submicron filtration without the use of precoats or filter aids in a vertical vessel with conical lower head for solids accumulation. This feature has the benefit of recovering small amounts of product from waste streams which can be returned to the process without contamination.

To deliver this unique capability, Auto-Pulse combines proven tube filter design and modern membrane technology installed in a highly permeable tube sheet that that has all the superior chemical and thermal characteristics of a candle filter operation. 


  • Because there are no precoats, polymers or other chemicals to be stored, mixed and dosed, AutoPulse is less expensive and easier to operate than other designs.
  • Since the filtration performance does not depend upon cake formation for fine solids removal, flows can be stopped and restarted without affecting downtime or effluent purity.
  • Micron rated elements and cloths that deliver unparalleled filtration quality and instantaneous clarity within a wide range of solids concentrations, from solutions as dilute as 0.002% to slurries with over 10% solids content.


When the service cycle reaches its end, cleaning can be performed using compressed air for backpulsing. After a number of cycles that last a few seconds, the solids are purged from the lower cone by flushing.

Depending on the properties of the membrane and the nature of the solids settled in the lower head, AutoPulse can also be “bumped” instead of backflushed as the flow through the tubes is momentarily reversed, dislodging the cake from the non-stick surface of the filter element. After the solids settle into the cone-shaped bottom of the extended filter shell, the influent is pumped into the filter just above the solids layer.

Because cleaning time is minimal, the filter is extremely flexible. Some applications will require only a small flow-equalization tank upstream to enable a single filter to handle a continuous stream. On larger filters, the top dome can be segmented to allow for cleaning in sections. This provides the key benefit of continuous filtration from a single filter.


Auto-Pulse filters are fabricated of a variety of materials ranging from coated carbon steel to Titanium and use a wide choice of engineered membrane materials from Teflon or HDPE coated to polymeric to ceramic for very difficult applications in the chlor-alkali, chemical or textile industries.

Auto-Pulse’s submicron filtration capability and tolerance to flow variations, make it unparalleled in its application to a wide variety of fine-filtration processes and high-solids waste streams which are currently treated by clarifiers, thickeners, filters, cartridges or combinations of these separation technologies.