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Holt of California offers two kinds of Diesel Particulate Filters (DPFs), Passive and Active, for diesel power generation.


A passive Diesel Particulate Filter is a filtration system designed to reduce particulate, carbon monoxide and hydrocarbon emissions. This solution can bring existing CAT 3400, 3500 and 3600 and "C" series diesel engines as well as other brands of diesel engines into regulatory compliance.

How it works:

A series of alternately blocked channels forces the exhaust gas to flow through the channel walls, where the particulates are physically captured and chemical reactions take place. Carbon monoxide and hydrocarbons are converted into carbon dioxide and water. Back-pressure is reduced though a process called passive regeneration that automatically removes excess particulate matter.

What a passive DPF does:

  • Particulate reduction greater than 85%*
  • Carbon monoxide reduction greater than 90%*
  • Hydrocarbon reduction greater than 90%*
  • Diagnostic module for back-pressure and exhaust temperature
  • Back-pressure less than 18 inches of water (critical grade silencer)
  • Alarm notification for high pressure levels

* When properly sized, clean, operating about 300°C and using ultra low sulfur diesel fuel.

Maintaining a Passive DPF
Many generators are being factory equipped or retrofitted with DPFs today to meet current emission regulations or bring existing diesel engines into regulatory compliance. With the addition of a passive DPF and added back-pressure, maintenance of the DPF is very important to avoid unnecessary shut downs. Load banking and removal of the individual filter blocks for offsite cleaning are offered by Holt and can greatly reduce back pressure issues.

Generators equipped with a passive DPF should have a diagnostic module to monitor exhaust temperature, back-pressure, time and date. These monitoring devices let you know when the filter needs to be regenerated. As with any maintenance item, the data from this device should be viewed on a regular basis and after any power outage.


Holt of California offers Rypos DPFs for your Active DFP needs. This Active DPF utilizes smart monitoring systems to predict when the DPF will need cleaning, and initiates an electrical regeneration cycle before your system is stressed by high back pressure. This filter is especially helpful for Tier 1 or earlier engines or those with many cold starts and varying loads.

How it works:

The Rypos active DPF consists of filter housing, flow control, electrical control circuit, and filter cartridges. The soot DPF itself is composed of sintered metal fibers shaped into filter elements and incorporated into filter cartridges. These cartridges are capable of capturing very fine carbon particles present in the exhaust stream, with high efficiency and high holding capacity. The DPF is regenerated through the presence of an electric current strong enough to heat the element to cause the collected soot to burn. This heating element and the filter are one and the same.

The filter's monitoring system analyzes readings every second to watch the rate of increase in back pressure. This way the system can predict when an Active cleaning will be necessary long before the back pressure reaches a level considered unhealthy by the engine manufacturer.

This Active DPF can be used alone or in conjunction with a diesel oxidation catalyst to reduce the soluble organic fraction, gaseous hydrocarbons, and carbon monoxide.

Maintaining Your Active DPF

The Rypos Active DPF maintains itself. Its operating costs are also much less than a passive filter.