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SYDFED-2X, SYDFED-3X, SYHDFED-1X | Product description
External pilot oil supply
Notes on dimensioning
Bosch Rexroth AG, Edition 11.2021, RE 30017-B
When using pump combinations
– NG45 with 45/28/18
– NG28 with 28/18
– NG18 with 18
in conjunction with the SYDZ pre-load valve on the main pump, there is a
mechanical conflict between port "P1" of the pre-load valve and the swivel
angle transducer housing of the built-on rear pump. For this reason, we suggest
that the main pump of the above combinations be equipped with an SAE flange
plate ¾" (NG28) or 1" (NG45) having a height of h = 45 mm. The construction
height of the pump assembly therefore changes by dimension "h".
An additionally built-on sandwich plate with shuttle valve automatically switches
the pilot oil supply between the internal or external pilot oil source, with always
the higher pressure level being selected.
A pump with external pilot oil supply can be recognized by
• the sandwich plate mounted below the pilot valve
• the hose routed around the pump case.
With external pilot oil supply, the actuating system of the SY(H)DFED pump works
independently of the actual high-pressure circuit, thus allowing an adjustment also
below an operating pressure of 12 bar within the range of "±100 %" (change in the
direction of displacement!).
When the control electronics is deactivated, the pump swivels to position
"-100 %" (motor operation) in an uncontrolled manner. This can lead to
cavitation and damage to the pump.
For this reason, special features are to be provided such as a pressure relief and
anti-cavitation valve as well as swivel angle actual value monitoring.
The pressure relief and anti-cavitation valve diminishes the risk of the pump's
running dry, the effects of which result in a reduction in the pump's service life.
The actual swivel angle value monitor could, for example, switch off the entire
drive or selectively shut off the pilot oil flow.
The following is valid for the actuating pressure:
Pilot oil pressure ≤ minimum operating pressure + 30 bar
Recommendation:
Further notes on the operation with external supply:
– In the case of external supply, the pump does not swivel to zero stroke when
the pilot valve is de-energized.
– Command values for pressure and flow must always be greater than 1 bar or 5
%, because there is no exact "zero" pressure or "zero" swivel angle due to drift
or inaccurate settings. For this reason, selections equal to zero or only slightly
greater can lead to cavitation in the worst case.
– In order to ensure sufficient lubrication for the pump system at all times, the
actual pressure value must not be less than 10 bar for longer than 10 minutes!
At a pilot oil pressure of 20 bar the brief pilot oil requirement during swiveling is
ca. 17 l/min, at 50 bar it is ca. 25 l/min. In practice, this amount of pilot oil is
needed only, if the operating pressure is less than 20 bar during the entire
swiveling process and thus the entire pilot oil demand must be supplied by the
external source.
In the steady-state, balanced condition, the pilot oil requirement is less than
1 l/min.
or
or
Absolute pilot oil pressure ≈ 20 bar
and
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