Filtration system
To prevent premature wear, ensure only clean fluid enters the hydrostatic transmission circuit. A filter
capable of controlling the fluid cleanliness to ISO 4406 class 22/18/13 (SAE J1165) or better, under normal
operating conditions, is recommended. These cleanliness levels can not be applied for hydraulic fluid
residing in the component housing/case or any other cavity after transport.
The filter may be located on the pump (integral) or in another location (remote). The integral filter has a
filter bypass sensor to signal the machine operator when the filter requires changing. Filtration strategies
include suction or pressure filtration.
The selection of a filter depends on a number of factors including the contaminant ingression rate, the
generation of contaminants in the system, the required fluid cleanliness, and the desired maintenance
interval. Filters are selected to meet the above requirements using rating parameters of efficiency and
capacity.
Filter efficiency can be measured with a Beta ratio (β
X
). For simple suction filtered closed circuit
transmissions and open circuit transmissions with return line filtration, a filter with a β-ratio within the
range of β
35-45
= 75 (β
10
≥ 2) or better has been found to be satisfactory.
For some open circuit systems, and closed circuits with cylinders being supplied from the same reservoir,
a considerably higher filter efficiency is recommended. This also applies to systems with gears or clutches
using a common reservoir.
For these systems, a charge pressure or return filtration system with a filter β-ratio in the range of β
15-20
=
75 (β
10
≥ 10) or better is typically required.
Because each system is unique, only a thorough testing and evaluation program can fully validate the
filtration system.
Please see
Design Guidelines for Hydraulic Fluid Cleanliness Technical Information
, 520L0467 for more
information.
Filter β
x
-ratio is a measure of filter efficiency defined by ISO 4572. It is defined as the ratio of the number
of particles greater than a given diameter (“
x
” in microns) upstream of the filter to the number of these
particles downstream of the filter.
Filtration, cleanliness level and β
x
-ratio (recommended minimum)
Cleanliness per ISO 4406
22/18/13
Efficiency β
x
(charge pressure filtration)
β
15-20
= 75 (β
10
≥ 10)
Efficiency β
x
(suction and return line filtration)
β
35-45
= 75 (β
10
≥ 2)
Recommended inlet screen mesh size
100 – 125 µm
Basic Information
H1 Axial Piston Pumps, Single and Tandem
System design parameters
©
Danfoss | April 2017
11062168 | BC00000057en-US0602 | 25
