Ball Valves on Low Pressure Dosing System Laterals

[carmengreen]

I am looking for opinions on the usefulness of installing ball valves on each lateral of LPD onsite sewage disposal system. We have been taught to provide these valves to allow the adjustment of the squirt height in each lateral. Some contractors have countered that this is an unnecessary expense. If the head loss through the manifold is considered to be negligible, they may have a valid case. If you have experience designing or installing these types of systems, I would appreciate your opinion: To ball valve or Not to ball valve?