Frequently Asked Questions
Q. What is a Hydro-Jet® Screen?
A. The Hydro-Jet® Screen is a self-cleansing, self-activating,
non-powered screening system for the removal of material >6mm
in two directions. The screen is designed to intercept and
retain aesthetically offensive material and gross solids
at all states of flow to the peak storm flow, with the material
being returned to the foul sewer during and after the storm
event.
Q. What advantages does the Hydro-Jet® Screen offer?
A. The Hydro-Jet® Screen is designed to operate as
a fully automatic, self-cleansing high performance
screening system. The main advantages of the Hydro-Jet® Screen
are that it has no moving parts and no power requirements.
This significantly reduces the maintenance commitment and
whole-life running costs. Rather than any form of mechanical
cleansing, the screen is kept clean by a dynamic backwashing
system produced by the hydraulic head present within the
sewer system (see flash animation for further details).
Q. What Hydro-Jet® Screen sizes are available?
A. Please use the following link to take you to the standard
Hydro-Jet® Screen configurations:
Hydro-Jet® Screen Drawing
Page
Flows from 1-450 l/s can generally be accommodated within
a rectangular chamber. Due to the size of siphon required,
flows greater than 450 l/s will require the L-shaped chamber.
Q. Can the Hydro-Jet® Screen be retrofitted within
existing chambers?
A. The Hydro-Jet® Screen has successfully been retrofitted
into many existing CSO's. Due to the specific restraints
of such projects the layout of the key Hydro-Jet® Screen
components (siphon, screen, weir etc) may differ from those
suggested in our standard arrangement. If a retrofit is being
considered then we suggest contacting Hydro direct with details
of the existing structure for confirmation of suitability.
Q. What is the maximum loading rate for the Hydro-Jet® Screen?
A. Following independent testing of the Hydro-Jet® Screen
at the national CSO testing facility at Wigan Wastewater
Treatment Works, the maximum recommended loading rate for
the Hydro-Jet® Screen is 200 l/s/m2 . This equates
to 150 l/s per screen panel.
Q. What is the return flow from the screenings return Hydro-Brake® Flow
Control? Is it always required?
A. The average flow rate through the screenings return Hydro-Brake® Flow
Control is in the order of 7.5 l/s for a 150mm outlet diameter
Type SXV. A 150 mm outlet diameter is the minimum recommended
size unit for use on foul and combined sewer systems. In
some instances there may be scope to increase the size of
the screenings return Hydro-Brake® Flow Control (>150 mm
diameter). This will however depend on the continuation flow
rate into the downstream sewer.
The screenings return flow control is an integral part of
the Hydro-Jet® Screen system. It is essential to restrict
the amount of flow that is returned to the continuation flow.
Without it, this flow component would increase from 7.5 l/s
(150 mm Type SXV) to c.~25 l/s. With less water flowing
to the siphon, the time taken for a backwash to occur will
increase thus reducing the backwash efficiency.
Q. What is the weight of a screen panel?
A. The weight of a single screen panel (1.215 x 0.641 m)
is 20 kg.
Q. What is the head loss imposed by the screen?
A. The Hydro-Jet® Screen is unlike weir mounted screening
systems/devices that impose an additional head loss on the
system that needs to be taken into account. The top water
level in the Hydro-Jet® Screen under normal operating
conditions is determined by the weir level and weir length
for a given flow rate since the siphon has a capacity in
excess of the incoming design flow.
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