Stop logs are in commonly used in water and wastewater treatment plants, lagoon control, flood control, and flow diversion. Historically, most stop logs are constructed of wood or metal. However, vacuum infused Fiberglass Reinforced Polyester (FRP) design is proving to be a much better solution for stop log design.
Wood swells as it takes on moisture, and the ends are easily damaged after which decay may start. Most of all, wooden stop logs are generally made from old growth redwood or cypress which is a diminishing resource. Metal stop logs are the most popular, but we find that they are too heavy for a solo operator to lift, hard to control leakage, more prone to theft and do not stand the test of time against corrosion.
When designing a new stop log arrangement, consider an engineered composite solution from Plasti-Fab, Inc. Plasti-Fab, Inc. designs each stop log specifically for each application. An engineered composite stop log is constructed of a copolymer composite totally encapsulating an internal reinforcing structure. The exterior surface is smooth and flat and the structure has no seams or joints thus assuring fluid tight integrity. It is highly corrosion resistant (25 year corrosion warranty), weather resistant, and requires little or no maintenance.
A stainless guide frame is designed for embedment in concrete, for surface mounting or mounting on channel walls. Surface mounted guide frames are often used on channel end walls. In these cases guides have slotted mounting brackets that slide onto preset anchor bolts making installation simple. A grout base is used to prevent leakage between the guide and channel wall. Installation in an existing channel requires an in-channel guide. This will reduce the channel width slightly. You may wish to chip out an embedment in the channel floor so the bottom guide can be flush mounted. A one inch grout base is recommended to prevent seepage between the wall and guide.
Properly designed guide frames and seals can provide for very tight shut off for seating or unseating heads. For leakage rates generally less than 0.1 GPM/ft. of wetted perimeter, make sure your guide frames have a neoprene UHMW seal with a double edged design that gives a point load seal against the face of the stop log. Alternatively, seals can be installed on the stop log for easier seal maintenance. Seals may be made of various elastomers, the most common being 60 durometer neoprene.
Smaller stop logs may be able to be installed and removed by a single operator. However, larger logs will likely require a lift or piece of machinery to remove them when installed with a full seating head. Properly designed logs are equipped with 1-1/2″ (typical) round stainless steel lifting pins that work in conjunction with a galvanized steel lifting beam. The lifting beam is built to automatically latch on to the stop log when lowered into the guide frame. The beam is released from the log by a simple tug on a rope tag line. When considering the amount of lifting force required to unseat a log you must consider the force of the water against, and possibly over, the stop log
Lifting force = weight of log + weight of lifting beam + force of water against it
The force of water calculated by:
Area of log that is submerged X head X weight of water in lb/cu. ft. X friction factor of seal
Head = the height of log divided by 2 plus any water above the height of log, if any
Weight of water = 62.4 lb/cu. ft.
Friction factor of neoprene seal = 1.1 (breakaway) & 0.7 (sliding)
5’ wide X 1’ tall = 95 lbs
Lifting beam weighs 200 lbs
5 sq. ft. X 0.5 ft. X 62.4 lb/cu. ft. X 1.1 = 171.6 lbs
Total Lifting Force For Breakaway = 95 lbs + 200 lbs + 171.6 lbs = 467.6 lbs
For more information on Plasti-Fab, Inc.’s engineered composite stop logs, download the brochure; or give us a call at 1-800-333-2252.