Recommended Operating Pressure Ranges; Maximum Operating Pressure; Relief Valve; Standard Precharge Pressure - Grundfos GT series Montage- Und Betriebsanleitung

When properly sized, the air/nitrogen cushion in the
GT will be of sufficient volume at minimum pressure
(pump cut-in) to allow a desired volume of water to
enter the GT with the subsequent pressure increase
within the specified operating pressure range as set
by the pressure switch.
This volume of water is equal to the average flow of
the pump during its minimum running time per start
as specified by the manufacturer.
The operation of the GT will then ensure that once
the pump starts, it will run at least the specified mini-
mum time before the pressure in the air/nitrogen
cushion of the GT reaches the pump switch cut-out
level, fig. 5.
3.5 bar
3.5 bar
3.5
3.5
Fig. 5
When this pressure is reached, the pump stops and
the system is fully pressurised. Further demand is
supplied by water in the GT. As water leaves the GT,
the air/nitrogen volume increases in the air/nitrogen
cushion and the pressure decreases, always equal-
ising the dropping system pressure, fig. 6.
3.0 bar
3.0 bar
3.0 3.0
Fig. 6
When the pressure in the GT reaches the minimum
point of the operating range (pump cut-in), the pump
switch actuates the pump and the operating cycle
begins again.
1.1 Recommended operating pressure
ranges
The GT tanks operate at any pressure range (pump
cut-in to pump cut-out) when properly sized.
The recommended pressure range for today's aver-
age residential system is 2.0/3.5 bar, fig. 7.
3.5
2.0
Fig. 7

1.2 Maximum operating pressure

The maximum operating pressure of the pump plus
the actual inlet pressure must not exceed the maxi-
mum operating pressure of the GT.
See nameplate.

1.3 Relief valve

A relief valve must be installed. The relief valve is set
to open at the maximum operating pressure. This will
protect the GT and other system components should
the pressure switch malfunction and fail to shut off
the pump. The relief valve should be installed at the
connection of the GT to the system piping and have
a discharge equal to the pump capacity at maximum
operating pressure.

1.4 Standard precharge pressure

See nameplate.

1.5 Pressure gauge

It is recommended to fit a pressure gauge to the pip-
ing system at the pressure switch.

2. Installation

2.1 Lifting the GT

The GT-D tanks have a tapped hole for the attach-
ment of a lifting eye.
The GT-U tanks have lifting eyes attached to the top
of the tank.

2.2 Proper GT location

The GT should be installed as close as possible to
the pressure switch. This will reduce the adverse
effects of added friction loss and differences in ele-
vation between GT and/or water main and switch.

2.3 Adjusting GT precharge pressure

This precharge pressure should be slightly below the
pump cut-in setting of the pressure switch.
The following steps should be taken:
1. Using a suitable pressure gauge, check pre-
charge pressure prior to assembling in system.
2. Release or add air/nitrogen as necessary to
make precharge pressure equal to pressure
switch pump cut-in setting.
Note: Check precharge pressure annually, but
ensure there is no water in the tank (switch off
the pump and open a tap).
3. Replace protective air valve cap and seal with
the air valve label provided. This will enable you
to determine if valve has been tampered with in
case of future service calls.
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