Solberg Oil Mist Eliminators - Manual (Page 2)

Solberg Oil Mist Eliminators 2
VAE Series: This product line is designed to remove all visible oil mist emissions. Many turbines and
compressors are designed to operate with the oil reservoir or crankcase maintained at a negative
pressure typically between -25 to -200 mm/1-4” of H20. The VAE uses a blower or fan (Item 1 on
schematic) to create vacuum and overcome the differential pressure created by the filter element. The
result is negative pressure inside the oil reservoir/crankcase. With the help of valves or a VFD
(Variable Frequency Drive), the negative pressure is controlled.
OPERATION
Pressure Differential & Efficiency:
Pressure differential is a very significant factor in designing OME’s for lube oil applications. This
value varies throughout the life of the OME, and will have an effect on controlling the pressure/vacuum
inside the reservoir/crankcase. The customer requirement determines the size of the internal filter
element and the size of the vacuum source.
Most Solberg OME filter elements are rated 99+% for 0.3 micron oil mist which typically results in
low outlet oil concentrations. The elements are sized properly, so the saturated pressure differential is
as low as possible. The increase in pressure differential from the initial reading to the saturated reading
should also be kept to a minimum.
Pressure differential is also an important consideration when specifying the blower or fan vacuum
source (from now on referred to as blower). Generally speaking, the greater the pressure differential,
the larger the blower must be. This is because it has to overcome the pressure differential of the filter
element to create negative pressure inside the lube oil reservoir or crankcase.
If the vacuum source ever fails, the VAE is equipped with a pressure relief valve (Item 3 on
schematic) that opens a 1” H20 of positive pressure.
Vacuum Regulation:
An important goal for plant personnel is to minimize maintenance and vacuum adjustments for the
VAE. The reservoir or crankcase is commonly maintained at a constant negative pressure, so the
blower must overcome the differential pressure created by the filter element.
Differential pressure increases as the filter element saturates and reaches equilibrium after a certain
time period (usually 48-72 hours). During this time of initial saturation the blower’s capacity to create
negative pressure is more than necessary. Also, over the element life span, it becomes dirty and
contaminated with particulate from the oil reservoir/crankcase. This causes an increase in differential
pressure, and the VAE vacuum level is increased to overcome this. There are different ways to control
this vacuum; the most common are listed below.
1. Using a Variable Frequency Drive (VFD) to vary the motor speed on the blower in
accordance with the required oil reservoir/crankcase vacuum level. This is accomplished
by using pressure transducers and has a control unit which automatically adjusts the speed
of the blower motor and thus the vacuum the blower can produce.
2. Using a filtered bleed in valve (Item 4 on schematic) to increase or decrease air into the
system so that the blower can create only the required negative pressure. This is done
manually and is the most common method used in the field.
3. Using a butterfly valve or damper to create pressure across the system so that it
compensates for the increased negative pressure. This is typically used in fan style
VAE’s.
Drain Port:
All the oil mist eliminators used to eliminate visible emissions are equipped with a drain port (Item 5
on schematic) so coalesced oil can be returned to the lube oil reservoir, crankcase or waste receptacle.
The drain line is typically supplied by the operator/end-user. The filter vessels are installed vertically;
thus the oil uses the force of gravity to drain. Below are two important considerations when installing
the drain line and VAE.
1. The drain line is under vacuum at all times; therefore, the drain line must be submerged
below the low oil level in the reservoir, crankcase or waste receptacle so oil mist does not
migrate up the drain line, into the vessel, around the element and into the atmosphere.