Variant Anti theft Air Valves

General

Variant combination air release and vacuum break valves protect pipelines from damaging vacuum conditions while ensuring that the system maintains design efficiency. The integral anti-shock feature provides protection against the damaging effects of uncontrolled filling and pump stoppages.

Functions

High capacity air discharge
High capacity air intake
Pressurized air release
Surge alleviation

Features

Optimum flow characteristics
Low pressure sealing
Compact design
No dissimilar metal corrosion

Operation of Variant Air Valves

Large orifice air discharge

During initial filling the pipeline is filled with air. As water is introduced into the pipeline, the air flows naturally towards the highest points along the pipeline. Air valves, positioned at these high points, allow air to pass freely through the large orifice to atmosphere.

Vacuum break

During scouring or when a pipeline ruptures, it is imperative that the pipeline is protected from damaging negative pressures. Variant air valves provide a full bore, unimpeded flow path that maximises the valve’s air intake capacity. The rapid inflow of air effectively prevents damaging vacuum conditions.

Pressurized air release

During normal operating conditions, air accumulates in the air valves, located at the high points along the pipeline. Once sufficient air has collected in the valve, the automatic float drops, opening the automatic orifice and allowing the air to escape to atmosphere.

Surge protection

Should pump stoppages cause water column separation within the pipeline, air is admitted rapidly through the air valve’s large orifice to protect the pipeline. As the water column returns, this air is then gradually discharged through the air valve’s anti-shock orifice. By restricting the discharge through the anti-shock orifice, sufficient air is retained in the pipeline to create a temporary surge accumulator. In instances where pipelines are filled too quickly, the anti-shock mechanism is blown shut by the excessive air flow. Air is now only released through the anti-shock orifice in a controlled manner, creating an air cushion in the pipeline. This air cushion slows down the approaching water column and absorbs any potential surges.

Anti-theft

Air valve theft adversely affects the reliability and efficiency of pipelines. This problem is compounded when multiple air valves are stolen from the same pipeline. The Variant models LN and LT were developed to prevent the theft of air valves thereby ensuring that the pipeline maintains it’s design and structural integrity.

Air Valve Selection

Sizing

The overriding criteria for air valve sizing is the intake requirement under vacuum conditions. To protect the pipeline and joints, it is necessary to limit the system negative pressure to 3.5m by admitting sufficient air into the pipeline as it empties. One needs to consider the pipeline diameter and gradient when calculating the required flow rate. Scour valve sizes and the rupture percentage of the pipeline are additional factors which need to be taken into account. Once the required intake flow rates have been calculated, the appropriate air valve can be selected from the following table.

Intake flow rates at 3.5 meters vacuum VALVE

VALVE SIZE	MODEL LN	MODEL LT
25mm	58 L/S
32mm	215 L/S
50mm	573 L/S
80mm	792 L/S	540 L/S
100mm		735 L/S
150mm		1865 L/S
200mm		3135 L/S

Although the air valve size is determined by the air flow required under the vacuum conditions, the flow rate (switching rate) at which the anti-shock mechanism is activated, needs to be considered to ensure that your pipeline will be adequately protected.

Orifice sizes and switching rates

SIZE MM	25mm LN	50mm LN	80mm LN	100mm LN	80mm LT	100mm LT	150mm LT	200mm LT
Anti-shock orifice	4	9	14	17	14	17	25	34
Inlet	25	50	80	100	80	100	150	200
Outlet	25	50	80	100	80	95	150	200
Switching Flow L/S	12	30	119	161	48	130	350	500

The LT can be supplied with a range of switching rates for each size.

Model LN Specifications

NOMINAL SIZE	MODEL NO	PRESSURE RATING	HEIGHT	DIAMETER
25mm Flanged *	025LN16	1600KPA	280mm	165mm
25mm Flanged *	025LN25	2500KPA	280mm	165mm
25mm Flanged *	025LN40	4000KPA	340mm	165mm
50mm Flanged	050LN16	1600KPA	275mm	165mm
50mm Flanged	050LN25	2500KPA	275mm	165mm
50mm Flanged	050LN40	4000KPA	316mm	165mm
80mm Flanged	080LN16	1600KPA	345mm	200mm
80mm Flanged	080LN25	2500KPA	345mm	200mm
100mm Flanged	100LN16	1600KPA	345mm	240mm
100mm Flanged	100LN25	2500KPA	345mm	240mm

*The 25mm valve has a 50mm mounting flange and should be installed above a 50mm isolating butterfly valve.

Working temperatures

4 – 75 Degrees Celsius.

Standard factory tests:

Automatic orifice operation.
Hydrostatic – 1.5 times working pressure.
Low pressure sealing – 20kpa.

End connections:

Flanged Valves: SANS 1123 studded

Type

Triple acting three stage

Material specification

BODY : Molybdenum Reinforced Nylon 11
AUTOMATIC FLOAT : High Density polyethylene
KINETIC FLOAT : High Density polyethylene
ANTI SHOCK FLOAT : High Density polyethylene
AUTOMATIC SEAL : EPDM
KINETIC SEAL AND O RINGS : Nitrile
SPACERS, STUDS, NUTS AND BOLTS : 304/316 Stainless steel

Model LT Specifications

NOMINAL SIZE	MODEL NO	PRESSURE RATING	HEIGHT	DIAMETER
80mm Flanged	080LT16	1600KPA	360mm	235mm
80mm Flanged	080LT25	2500KPA	360mm	235mm
80mm Flanged	080LT40	4000KPA	450mm	235mm
100mm Flanged	100 LT16	1600KPA	360mm	235mm
100mm Flanged	100LT25	2500KPA	360mm	235mm
100mm Flanged	100LT40	4000KPA	450mm	235mm
150mm Flanged	150LN16	1600KPA	510mm	370mm
150mm Flanged	150LN25	2500KPA	510mm	370mm
150mm Flanged	150LN40	4000KPA	575mm	370mm
200mm Flanged	200LT16	1600KPA	590mm	410mm
200mm Flanged	200LT25	2500KPA	590mm	410mm
200mm Flanged	200LT40	4000KPA	650mm	410mm