How to keep the loading dock dry and safe.
The 'funnel effect'
Water infiltrates docking areas due to the "funnel effect," which occurs when water is channeled down the roof of a semi-trailer directly onto the dock. The condition is often caused by a declined dock approach, when the rear of a trailer positioned at the dock is lower than the front. Water on the top of the trailer simply follows gravity and flows off the top, often beneath an existing seal or shelter, fight into the loading-dock area.
Standard dock seals and shelters--primarily fabric structures that surround the top and sides of a loading-dock door opening--can help a company save on energy costs and increase worker comfort. But as anyone who has ever worked in a dock area can attest, these seals and shelters can't do it all.
A successful solution
Preventing water infiltration caused by trailer-funnel effect requires that water be blocked by using the fight amount of pressure in the right place. Specifically, sufficient pressure is needed on the top of the trailer across its full width and in front of the area where a standard head pad or curtain is located. To address this situation, Frommelt Products Corp. introduced the rain-diverting header seal in the 1990s. Other companies soon followed with similar solutions.
Rain-diverting header seals are comprised of a sealing member made of foam, wrapped in protective fabric and held in place by a frame. The sealing member, which may be a block or cylindrical shape, is suspended above the dock door, where it makes contact with the top of a trailer as it backs into the dock. A rain-diverting header seal can be equipped over an existing seal or shelter, or can be installed as a stand-alone unit.
All rain-diverting header seals work in the same general way: As a trailer is backed into the dock, the sealing member automatically contacts and rests with pressure upon the top of the trailer, creating a barrier that diverts flowing water off the sides of the trailer roof.
How to choose
Not all rain-diverting header seals are designed the same. Here are three purchase considerations:
Trailer coverage. A rain-diverting header seal must form a tight, consistent seal regardless of trailer height or position in order to perform properly and reliably. To do so, the seal should provide broad trailer coverage range, optimally 15 in., to accommodate typical trailer traffic with heights from 12 ft. 3 in. to 13 ft. 6 in. Some rain-diverting seals offer coverage ranges of 9 in. or less, meaning shorter trailers get less, or no protection.
Seal pressure. Based on how it is created, seal pressure and effectiveness varies. Some seals use weight and gravity. The compressible sealing member is weighted and flexibly suspended to be automatically positioned and create a customized seal on each trailer that enters the dock. The weighted seal resting on top of the trailer ensures that the same amount of pressure will be applied to all trailers, regardless of height or position.
Others use the trailer itself to create the pressure. In this case, rectangular foam blocks are affixed to a frame and are bent into place on the trailer top when the trailer backs into the dock. The height of the trailer dictates the amount of pressure to be applied. Greater pressure is applied to taller trailers; less to shorter trailers. Canted trailers (when one side is lower than the other) are best sealed by weighted units that are able to flexibly adjust to trailer position yet retain maximum pressure across trailer width.
Durability. Check to ensure that the rain-diverting header seal is engineered for longevity. Some, for example, use front-impact plates made of semi-rigid material that absorb the impact from incoming trailers and protect the more flexible sealing member. Others do not, leaving the sealing member vulnerable to damage from repeated impact. Also consider how the header seal framing responds under impact from off-center trailers coming in higher than expected. Some seals are equipped with pivoting headers that protect the unit from damage in such situations.
Frommelt Products Corp.
Use InfoLINK 069-60301-104 or Call 800-441-6180
Chuck Ashelin, Director of Engineering, Frommelt, Products Corp., Dubuque, IA