Page 56 - Council Journal Winter 2019

FEATURE Development in Poor Soils A revision to the 2009 Code of
network and spread over the percolation area more effectively than by a gravity system. This means that pressure must exist to the furthermost part of the network; otherwise the percolation area is only being partially dosed which can quickly result in leakage and overloading.
system design. For this reason, site-specific design proposals are necessary for wastewater pressure systems, and they should be installed and operated by people with knowledge of the importance of the design principles.
Practice is planned by the EPA following the review of the report with an estimated timescale of December 2016 to have a document available for public comment. Based on previous experience, it is reasonable to expect that the recommendations of the report will largely be incorporated into the new guidelines and then into Part H of the Building Regulations.
Pressure systems by their nature function by maintaining sufficient pressure throughout the network while taking account of the pressure release points and length and volume of pipes in the network. Similarly, in a pipe network that supplies wastewater to a polishing filter or any pumped system, a balance must be maintained between the pump capacity, the volumes of pipes, the number of orifices and the diameter of the orifices.
“Due to variations in the discharge rating of pumps available on the market, it is important to correctly match the orifice diameter and the lateral diameter in the distribution system to the pump, thus ensuring even and effective distribution of the hydraulic load across the fillter area,” according to EPA regulations.
Conventional percolation trench systems rely on gravity to spread the wastewater through the percolation area. Even using a distribution box or other flow splitting devices gravity systems can only partially distribute water over the percolation area. Some segments will consistently receive a larger volume of water.
Low pressure pipe networks
This is also essential for LPP system pipe networks as they are calculated on a similar basis. For larger non- domestic systems, calculated network designs with pump and network dose volume specifications are even more important.
On sites with suitable soil conditions, this is satisfactory and can provide long term passive soil treatment. But the percolation area is only being partially used when compared to a pressure system.
This requires the system designer to control the number and size of holes or orifices in the pipe network; otherwise the required design pressure will be released before the ends of the perorated pipe laterals. Similarly, by specifying the number and diameter of pipes the volume of water to be pumped through the pipe network must be part of the overall
To maintain the design pressure in the pipe network, the number and diameter of orifices must be matched by the capacity of the pump and the volume of water pumped each time the pump runs.
The advantage of a pressure distribution system is that the water can be pumped throughout the pipe
Site variables also affect performance such as site elevation, distance to be pumped and diameter
Low Pressure Pipe Unit
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