Viking VFT - The Safety Thermal Relief Valve

BLADDER TANK MODEL VFT & FT
INSTALLATION, OPERATION AND
MAINTENANCE MANUAL
(
foam concentrate inside the bladder
)
TECHNICAL
MANUAL
F_032216 16.1 | TM1.3.1.1/14032016/en
The Viking Corporation, 210 N Industrial Park Drive, Hastings MI 49058
Telephone: 269-945-9501 Technical Services: 877-384-5464 Fax: 269-818-1680 Email: techsvcs@vikingcorp.com
VISIT THE VIKING WEBSITE FOR THE LATEST EDITION OF THIS TECHNICAL MANUAL
Page 10 of 35
3.4 The safety thermal relief valve
The standard design pressure - and maximum working pressure - of Viking bladder tanks is 175 psig (12.1 barg) unless otherwise
stated. Please always refer to the bladder tank nameplate placed on the shell to determine the design pressure. It is the
responsibility of the end user to provide a primary pressure regulating / relief valve, of suitable set-point and capacity, resulting
from a specic calculation, to protect the tank from rapid over-pressurization. Details of the entire re protection systems design
must be known, such as water pressure and ow capacity, to size this primary pressure regulating/relief valve.
Thermal expansion of foam concentrate and water inside the tank can also generate a pressure exceeding the rated capacity. This
slow but steady pressure increase could result in problems ranging from leaks at threaded or anged connections to a serious
physical damage of the bladder or pressure tank. For this reason a safety valve, called the thermal relief valve, is installed on all
Viking bladder tanks (see item no. 3 in gure 3.3.1.). This valve is not intended to protect the tank from an overpressure
generated by the re ghting network system, as the latter depends on the pump(s) owrate, total pump(s) head and on the
static (geodetic) pressure arising from the bladder tank elevation. This data is normally unknown to Viking and therefore outside
Viking’s scope of work.
The thermal relief valve’s only function is to prevent an over-pressurization which the isolated and self-standing bladder tank may
experience due to the volume change of its content. The thermal relief valve is provided with a locking seal that prevents pressure-
setting modication after the equipment has been despatched from the Viking factory. For any technical detail on the thermal relief
valves, please refer to the data sheet and certicates supplied by Viking.
To prevent or minimise the effect of thermal expansion, which may result in water discharge from the thermal relief valve, it is
recommended to:
1. Avoid lling the tank with cold concentrate. If possible, allow the concentrate to warm-up to room temperature and, in any case,
do not ll the bladder tank above its nominal volume if temperature increases are envisaged (the bladder tank has an effective
volume higher than the nominal. This allowance permits the foam concentrate expansion to be relieved by the thermal relief
valve placed on the water side).
2. Install a sun canopy to protect tanks installed outdoors.
3. Avoid tank exposure to high temperatures.
To prevent unwanted water discharge on the surface of the bladder tank, which may result, after a period, in a painting damage, the
thermal relief valve should be preferably piped to a drain. If piped, make sure that the piping does not limit the discharge capacity
of the thermal relief valve and consider the use of a drain cup or sight glass to give a visual indication of any thermal relief valve
activation