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Return Line Filter: The Ultimate Guide
Return Line Filter: The
Ultimate Guide
In today’s guide, you will learn both the basic and
advanced concepts of return line filters.
It will help you choose the best return line filter for
your system, preventing costly and unnecessary
system contamination.
Among the key things, you will learn here include
definition, symbol, function, installation, and
criteria for selecting a return line filter.
Let’s have a look.
Return Line Filter Basics
This section covers the most basic concepts of
return line filters.
Even before you think of buying return line filters,
here are a few things you should know:
· What is the return line filter?
Return line filter refers to a type of filter that is
common in open loop applications.
They serve the function of filtering the fluid before
it flowing back to the hydraulic reservoir.
Return Line Filter
Return line filter – Photo courtesy: Modern
industrial hydraulics
By doing this, return line filters help in keeping the
reservoir clean by removing all the dirt particles.
Also, filtering the fluid before it flows into the
hydraulic system enhances the operational
efficiency of your application.
· Return line filter symbol
Return line filter symbol offers a clear
representation of every component and their
function.
It is, therefore, crucial to understand these
symbols since they will aid in understanding
return line filter components and how they work.
These symbols are essential in depicting the fluid
flow on the return line filter as well as the
components that make up a return line filter.
Thee symbols need to adhere to the industry
standards such as DIN24300, ISO1219-1, and
ANSI Y32.10.
Here is a look at these symbols for better
understanding.
Return line filter symbol
Return line filter consisting of a bypass valve and
an electrical clogging indicator
There are different characteristics that a return
line filter represent.
That is, the function, the number of connections,
the operating principle of the return line filter as
well as the switching position
It is therefore vital that when coming up with a
return line filter, you consider all the components.
Also, the function of the bypass valve is to prevent
the fluid from flowing backward before filtration
takes place.
· Return Line Filter Function
As we have seen earlier, the essential function of
a return filter is to filter the fluid before it returns to
the hydraulic reservoir.
Hydraulic filter
However, a return line filter serves other functions
including:
· Filtration of your fluid
There are several contaminants present in your
fluid which can hurt the fluid performance.
Some of these contaminants are small in size to
be seen by the naked eye.
However, you can increase the performance of
your fluid through filtration by using a return line
filter.
The availability of different filter element sizes for
your return line filter makes them ideal for fluid
filtration.
· Ensures the smooth flow of
your fluid
Imagine how many times you would have to stop
your hydraulic system from removing the
contaminants that hinder its operations.
Perhaps it will take you long to finish a particular
task.
However, you can eliminate these disruptions by
using a return line filter which filters all these
contaminants.
This results in a smooth flow of your fluid in a
hydraulic system.
· Protection of the hydraulic
system
A return line filter protects your hydraulic system
by filtering unwanted particles from your fluid.
This has the effect of extending the productive life
of your hydraulic system.
Where to Install a Return Line Filter
There are several factors that you need to
consider before selecting where to install your
return line filter.
They include the hydraulic system cleanliness
requirements and the location of the component
that needs protection.
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Valve
PressureFier
1-5Micron
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RetumLineFiter
3-25Micron
15-50PSIBy-pass
SuctionStrainer
40-150Micron
1-3PSIBy-pass
Return line filter with by-pass valve
You may also consider the pressure of your
application before deciding where to locate your
return line filter.
Different types of return filters are available for
different location points.
However, in practice, you can install your return
line filter either on the inside of your reservoir or
in-line with your reservoir.
Always consult with your manufacturer before
deciding on the perfect location of your return line
filter.
Types of Return Line Filters
Even though return line filters have a basic
working principle, there are different types that
you can find in the market.
You, therefore, need to select the model that best
fits your application.
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Return line filter with clogging indicator
For better understanding, let’s have a look at the
different types of return line filters available.
· Tank mounted return line filters
As the name suggests, the design of tank
mounted return line filters allows for the
installation and fitting on hydraulic fluid tanks.
Here, their primary function is to filter solid
particles from the fluid ensuring clean fluid flow.
Alternatively, a tank mounted return line filter can
function as a bypass filter for your hydraulic
system.
A tank mounted return line filter consists of
various components which work in hand to ensure
smooth filtration of your hydraulic fluid.
These components include a filter bowl, a cover,
filter element, bypass valve, a maintenance
indicator, and an electronic switching element.
Also, depending on the size of your tank mounted
return line filter, you may have a breathing filter, a
surge protection unit and a return pipe.
The working of these components is similar to that
of a regular return line filter.
· Double tank mounted return line
filters
Double tank mounted return line filter is a type of
filter that consists of two return filters joined
together using a bypass valve.
These filters are ideal for mounting on hydraulic
fluid tanks with a large operating capacity.
They function just like any other return line filter
with the only difference being their operational
capacity.
The fact that they double to allow for
simultaneous filtration of your fluid ensuring
continuous operation of your application.
When clogging happens on one return line filter,
the bypass valve closes directing the fluid to the
other filter.
This allows you to clean the clogged return line
filter while the operation of your application
continues.
Double tank mounted return line filters are ideal
for an application that requires a continuous flow
of fluid or larger applications.
· T-types return line filters
T type return line filter gets its name from its
shape which is like a T.
Their design allows them to be a perfect fit for
filtration of fluid with low pressure.
The reason for this is because fluid flows into the
return line filter creating a high pressure which
aids in fluid filtration.
There are different sizes of T type return line
filters available for selection depending on the
size of your application.
It is vital that you select one that fits your
application to avoid incidents of not having
enough pressure for filtration to take place.
Criteria for Selecting Return
Line Filter System
There are several return line filters available for
your selection depending on your application.
However, you need to consider several factors
before picking one.
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coveronlyonversion
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typecodelabel
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indicator(typeVR)
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inlet
outle
Return line filter design – Photo courtesy: Hydac
Among these considerations include:
· Maximum pressure
The maximum pressure a return filter can handle
during the filtration process is a vital factor when
selecting your return line filter.
Too much pressure past the given limit has the
effect of causing rupture to your filter element.
Also, it may have the effect of your pocket filter
not filtering well as a result of too much fluid
passing at a given time.
As such, when selecting a return line filter, you
need to ensure that the pressure of your return
line filter matches that of your hydraulic system.
· Flow rate
The flow rate of your return line filter is a crucial
factor that you must take into account.
Different return line filters have different flow
rates.
When selecting a return line filter, you need to
ensure that it has the same flow rate as that of
your hydraulic system.
A flow rate ensures uniform flow of your fluid at a
given point over time which maximizes the
filtration process.
By having the correct flow rate for your return line
filter, you can ensure maximum filtration of your
fluid.
· Size of your return line filter
element
The size of the return line filter element plays a
vital role in determining which return line filter to
select.
As you know, not all the contaminants have the
same size; as such, you need to pay attention to
the size of the filter element.
The size of the filter element will determine the
filtration level of the fluid.
· Filter ratings
Every return line filter has a rating that determines
how effective it is at filtering your fluid.
You need to consider this when selecting a return
filter for your fluid.
This is what will determine the effectiveness of
your filtration and also have an impact on the flow
of your fluid.
· Dirt holding capacity
The dirt holding capacity is another consideration
that you need to consider when purchasing your
return line filter.
Dirt holding capacity – Photo courtesy: Eaton
It is vital to note that a larger dirt holding capacity
minimizes the number of times you have to stop
your application for unclogging purposes.
On the other hand, a small dirt holding capacity
return line filter implies that you will have to
interrupt your application frequently.
It is therefore vital that you select a return line
filter that has the correct dirt holding capacity for
your application.
· Type of your fluid
Fluids have different characteristics which you
must consider when selecting your return line
filter.
These characteristics affect your return line filter.
For instance, the viscosity of your fluid affects
your return line filter since it affects the flow.
You, therefore, need to ensure you either have a
return line filter that has a large filter element of
has high pressure.
Also, the temperature can affect your return line
filter.
You need to ensure that your return line filter
meets the given temperature of your hydraulic
fluid.
If the temperature of your fluid is high, it is
advisable that you select a return line filter that
has a higher temperature than that of your fluid.
The purpose of this is to prevent the filter element
from rapturing which may lead to malfunctioning
of your return line filter.
It is therefore vital that you select a return line
filter that matches the characteristics of your fluid.
Return Line Filter Assembly –
Understanding Return Line
Filter Designs
Understanding the components of a return line
filter is crucial in knowing its assembling process.
Through this, you will be able to know how the
different parts work together in ensuring the
efficiency of a return line filter.
Different types of return line filters – Photo
courtesy: Fluiden
Here is a look at these components in detail.
· Return line filter head
This refers to the topmost of the return line filter
that is portable.
It serves as the mounting pad while installing on a
machine.
· Inlet and outlet points
On the filter head, you will find the inlet and outlet
points.
They are crucial points during the filtration of your
fluid since they serve as points through which the
fluid enters and exits the filter.
Dirty fluid flows through the inlet for filtration to
take place and clean fluid leaves via the outlet.
· Filter housing
The filter housing refers to the outer casing that
holds the components of the return line filter
together.
Different materials make up the filter housing.
However, an effective filter housing material is
one that can withstand the environmental stress in
which it operates.
· Filter element
The filter element refers to the inner part of the
return line filter where actual filtration takes place.
As fluid flows through the return line filter, it
passes through the filter element where filtration
of contaminants takes place.
· Dirt holding bowl
After filtration, clean fluid flows out of the return
line filter via the outlet while the contaminants flow
to the dirt holding bowl.
This happens continuously until the clogging
takes place on the filter element.
· Discharge valve
At the bottom of the return line filter is a discharge
valve that serves as the exit point of the
contaminants.
After filtration, you need to clean your filter to
remove the unwanted particles.
· Bypass valve
A bypass valve is a valve located between the
inlet and the outlet on the filter head.
The function of the bypass valve is to protect the
system in case your filter is clogged.
This allows you to clean your return line filter.
Working Principle of Return
Line Filters
The basic principle of how a return line filter works
is quite easy.
Once you have identified each part, you won’t fail
it understand how it works.
Working of hydraulic filters – Photo courtesy:
Machinery and Hydraulic
This is crucial not only when it comes to the
operation of the device but also during its
maintenance.
Here is a look at how this device works.
First, fluid flows into the return line filter via the
inlet which is mostly at the top but depends on the
design of your filter.
This flow is generally of high pressure that forces
the fluid into the filter element.
As it flows through the filter element, the filtration
takes place via the filter mesh.
It is therefore essential to consider the sizes of the
filter mesh before selecting a return line filter for
your application.
After filtration, the filtered fluid flows out of the
return line filter via the outlet while the
contaminants flow downwards to the dirt collecting
duct.
There are different sizes of the dirt collecting duct
for selection depending on the size of your
application.
The bypass valve available minimizes the risk of
having unfiltered fluid from flowing back to the
hydraulic system.
The filtration process continues until clogging
takes place.
At this point, you have to clean the filter element
and the filter itself.
There are several ways of cleaning your return
line filter.
However, the most common is the self-cleaning
backwash option.
It involves allowing the flow of water in reverse
through the filter element which removes all the
contaminants.
The contaminants flow to the dirt holding duct and
out through the drainage valve.
How to Install Return Line
Filter System
After purchasing a return line filter and before it
starts operation, you need to install it on your
application.
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