Home » GamGram Collection » No. 57 / FILTER ACCESSORIES / APRIL 2006



I went to visit a customer a years ago who had just completed a fuel . Although he had purchased his filters from a competitor of mine, I was happy to take "the guided  tour''. When I saw the filter vessels, I immediately realized why I had not been competitive- my customer had bought vessels without any accessories.

I had to explain carefully to this man what each accessory was for and why it was necessary. When he was done properly "outfitting" his filters, he had spent a lot more than he expected.

The correct accessories are critically important for proper performance and safe operation of any filter vessel. The following is a brief overview of common accessories. Also in GamGram #37 on the recovery of fuel released by air eliminators, pressure relief valves, and automatic water drain valves.

1. AUTOMATIC AIR ELIMINATOR (AAE)- This device releases trace air from the filter vessel. Without an , air w be trapped in most filters or filter separators, unless they have the fuel outlet connection on the top or a similar design prevents air from accumulating  such as the small Velcon VF-61 filter vessel.
Without an automatic means for ing , it accumulate such an extent that the upper portions of elements are continually exposed and never do any filtering and potentially cause a fire in the vessel (See GamGram #15). operator no way of knowing this.

2. AIR ELIMINATOR CHECK VALVE- A rubber sealed (so -seated) check with a low "breakaway pressure" allows air to exit the AAE, but prevents or contamination in the outlet piping from going backwards into the vessel. We've seen many drain back problems (where the vessel empties to the underground storage tank, or low aboveground through an open or leaking line valve). We have also seen a situation where diesel el entered an avgas system this way. See GamGram #43 for outlet piping information.

3. MANUAL AIR RELEASE VALVE- This is usually an ordinary ball valve, connected in parallel with the . It allows easy draining of the vessel for element changing by providing a pa for air to enter the vessel. It also allows air to be released manually r changing elements, but care must used to prevent spillage. You may want this valve to be likable.

4. PRESSURE RELIEF VALVE (PRV) - A PRV is a required  accessory on any filter vessel. It is solely up to the vessel from pressure build-up caused by the sun's heat. It is also called a thermal relief valve. Without a PRV, thermal build-up break the vessel housing, cause leaks, or similarly damage other adjacent components such as meters or hoses. We have seen thermal build­ up create pressures over 1200 psi in a 75 psi system.

5. MANUAL DRAIN VALVE- All filter vessels must have a manual drain valve, or it is impossible to properly drain the vessel to change elements or conduct periodic sump inspections. (See GamGram #2 and #5.)

You may want  this valve to be lockable, or to be spring loaded valve, which closes  automatically when you release the handle. Another good addition is a lock connector with a dust cap which not only keeps the outlet clean, but serves a secondary spill prevention device and allows a hose to be easily connected.

6. DIFFERENTIAL PRESSURE GAUGE-- All filter vessels should have a differential pressure gauge or indicator so that you can determine the condition of the elements and avoid the possibility of bursting dir elements. The only possible exception is a vessel that is d by a pump incapable of delivering over 25 psi under any circumstances and that is a 'judgment call". A low pressure pump cannot burst a properly designed and built element. The preferred indicator is a dire reading, piston- type differential pressure gauge with an inlet filter. An alternative is a pressure gauge with a p per selector valve. See GamGram # l. A differential pressure control system is recommended for all water absorbing element vessels and also un end filters.

7. SAMPLING CONNECTIONS- All jet fuel filters should have inlet and outlet stainless steel sampling connections with sampling probes to ensure that representative samples can be obtained. By comparing the inlet and outlet results you can ascertain performance. Avgas systems can also bene t from such connections, but they are not essential except on jet fuel.

NOTE: the following accessories apply only to filter separators.

8. WATER CONTROL -This is a large subject, worthy of a GamGram  of its own. In short, a filter separator without a proper water control device able the system flow if water collects in the sump, is just a filter. This is because it may remove water, but once the sump of the filter separator is ll of water, any additional water enter the vessel goes downstream.
A water control device should positively stop el the ow. A water control device be electric, hydraulic or pneumatic. It may be t ope ted or (if electric) of the conductivity probe. Electric water controls should be intrinsically and/or explosion proof  except for truck mounted systems allowed to be weather-tight by l l regulations, such as in the USA. e water control may stop flow by turning on the pump or by causing an outlet  control valve (slug valve) to close.

9. SUMP/DRAIN HEATER- In climates where air temperatures go below the freezing point, a heater is necessary to prevent water from freezing in the drain valve. A heater should be explosion proof. have a built-in adjustable thermos, a ''water  density" no higher than 22 watts/in2, and stainless steel heating element. A large vessels or vessels where the water control may become trapped in ice, a sump heater may also be needed. For more information on is subject, see GamGram #30.

We recommend the above list equipment as a minimum. Be sure to me the requirements  of your oil company and/or airline. Also make sure to use the appropriate material. We recommend against the use of cast iron accessories.