Mankenberg NV 93 Betriebsanleitung Seite 13

Know How Float Valves
Level controllers and float valves control the liquid level in a vessel
Level controller or float valve
You should use a level controller with float chamber if the float cannot
be mounted in the vessel. It is mounted in the pipeline and connected to
the vessel by means of balancing lines.
Float valves have no float chamber. The float is always mounted in the
vessel.
Feed and drain valves
Feed valves (code letter "Z") close as the float rises and prevent
overflowing. Drain valves (code letter "A") close as the float sinks and
ensure that the liquid level does not drop below the required level.
Mounting of float-controlled valves
- Float valves for installations in vessels are mounted inside the vessel
complete with float.
- Float valves for installation on vessels are flange- mounted on the outer
skin of the vessel.
- Float valves for installation in pipe lines are installed in the feed/drain
pipe.
The float lever either projects into the vessel or the float movemen´s is
transferred by means of a cable.
Flow direction of float valves
The flow direction determines the mounting arrangement and type of
float lever used:
- horizontal, flow direction towards or away from the vessel code letter
"w"
- vertical, flow direction upwards code letter "o")
- vertical, flow direction downwards (code letter "u")
Selecting valve type and nominal diameter
To select the valve type and determine the required nominal diameter
you should calculate first the operating performance parameter K
on the maximum operating values and minimum pressure drop Dp. You
should choose a valve having a K
calculated K figure.
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Selecting the operating pressure range
The maximum operating pressure of your system must be within the
operating pressure range of the valve; if not, the float valve will not close
or open.
Pressure inside the vessel
Check whether the vessel in which the float is to be mounted is not
pressurised. If the vessel is pressurised a pressure-resistant ball float has
to be fitted. Cylindrical floats may only be used in non-pressurised
vessels.
Temperature
If the valve is to be used for temperatures above 80 °C or a liquid other
than water, the compatibility of the elastomers must be checked. For
hydrocarbons like gasoline, petrol etc., for example, the valves are fitted
with FPM elastomers, whilst for higher temperatures they are fitted with
EPDM or, if necessary, with a metallic cone seal.
Adapting the float
Float valves are normally designed for media with the specific gravity of
water. By choosing a different float geometry, by filling the float or by
altering the operating pressure range, we can adapt the floats to other
media.
Balance and double seat
Single seat non-balanced float valves are used for low pressures. They
are relatively insensitive to contamination and dirt deposits.
Single seat balanced valves can be used for larger pressure drops and
feature smaller floats.
Double seat valves are specially suitable for large flow rates.
Overflow preventers
A special product are the PTB-approved overflow preventers Types 36S
and 36SF. These are mechanical safety devices for flammable liquids.
value which is 30 % greater than the
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Valve seat leakage
These valves are no shut-off elements ensuring a tight closing of the
valve. In accordance with DIN EN 60534-4 and/or ANSI FCI 70-2 they
may feature a leakage rate in closed position in compliance with the
leakage classes II – V:
Leakage class II (metal sealing double seat cone) = 0.5% Kvs value
Leakage class III (metal sealing cone) = 0.1 % Kvs value
Leakage class IV (PTFE seal cone) = 0.01 % Kvs value
Leakage class V (soft seal cone) = 1.8 x 10-5 x Δp x D* [l/h]
*D=seat diameter
Any low leakage requirement must be expressly specified when ordering.
Valve leakage can be considerably reduced by special measures such as
lapping the valve seat, using special cone seals and increasing the valve
closing force by changing the lever geometry or increasing the size of
the float.
Adjustable filling level
In the case of valves fitted with float rod and adjustable float, the level in
the vessel can be adjusted by sliding the float along the rod.
Float rod guide
For float rods a guide must be provided in the vessel to prevent the float
oscillating. Float valves with parallel guide or special designs featuring a
top-mounted float do not require a rod guide.
Operation
Make sure that no pressure surges or water hammer occur in the
system, which could destroy the float. In the case of foaming media and
the resulting reduction of the specific gravity, a float valve cannot
operate reliably. In this case a foam abatement circuit should be
provided.
based Maintenance
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Float valves and level controllers should be cleaned and serviced at
regular intervals. This rule applies especially to valves which are rarely
operated e.g. valves fitted in sprinkler systems.
Thorough cleaning is important in the case of liquids containing
substances which easily form deposits (such as iron, lime, suspended
solids etc). Sand and abrasive particles carried along in the liquid can
cause rapid wear. Please ask for specially adapted valves.
Valves free of oil and grease or silicone
Please pay attention to order an fit only spares free of oil and grease
resp. free of silicone.
Please consult our engineer if extreme operating conditions apply
or whenever you are in doubt.
Notes on Safety, operarting instruction etc. MUST be followed.