Fresenius Medical Care 2008K Troubleshooting Manual page 203

PHT- 10.2.0 CHECKING VALVE #28
Referring to the Figure (right), unplug valve #28 from the
distribution board. Does the valve continue to leak?
Yes Replace valve #28 (leaking).
No Replace the actuator board (see
page 8).
Automated Pressure Test Theory:
A leak in the secondary hydraulic circuit compromises accurate fluid (UF) removal. The following
discussion describes how the automated Pressure Tests are performed.
With the balancing chamber (BC) valves cycling normally and the flow pump running the Automated
Pressure Tests (Negative Pressure, Positive Pressure) begin with "Get Neg TMP". During this time the UF
pump #22 strokes until a 'target' of approximately -240 mmHg (TMP = 240 mmHg) is achieved as
monitored by the dialysate pressure transducer #9. This normally takes less than one minute. When target
pressure is reached the UF pump stops. After a stabilization period "Neg Flow On" begins and runs for
one minute. If pressure remains stable (+/- 20 mmHg) the test passes. Next all four 'fresh side' BC valves
open briefly to drive positive (loading) pressure into the secondary circuit. At this point all eight BC valves
are closed and the flow pump (#21) stops. Because target pressure (approximately +300 mmHg) is
overshot the UF pump strokes, two to four times, until target is achieved. After a stabilization period "Pos
Flow Off" starts and runs for one minute. If pressure remains stable (+/- 30 mmHg) the test passes.
Probable Causes of Automated Pressure Test Failures (Neg Flow On, Pos Flow Off):
UF Pump cannot create target negative pressure
Air entering or water escaping through a bad o-ring, bad connection, tubing leak, etc.
Dialysate Pressure (or Transmembrane Pressure (TMP) out of calibration specifications)
If equipped, DiaSafe
Deaeration pressure too high or too low
Valve #43 leaking internally
Balancing chamber valve (#31 through #38) leaking internally
The On Line Pressure Holding Tests (On Line PHT), if activated, are performed automatically every 12
minutes (720 seconds) regardless of other alarm conditions. These tests monitor the current dialysate
pressure (i.e. pressure is not created as it is during Negative Flow On/Positive Flow Off Pressure Tests).
Dialysate flow is momentarily defaulted to 500 ml/min, valve #26 opens and valves #24 and #25 close (to
isolate the dialyzer, if attached). Dialysate pressure is monitored for two consecutive balancing chamber
cycles, approximately 7.2 seconds. If pressure remains stable (+/- 30 mmHg) the On Line PHT passes.
Probable Causes of On Line PHT Failures:
Air entering or water escaping through a bad o-ring, bad connection, tubing leak, etc.
If equipped, DiaSafe
Valves #43, #24, #25 leaking internally
Balancing chamber valve (#31 through #38) leaking internally
Deaeration pressure too high or too low
Dialysate Pressure (or Transmembrane Pressure (TMP) out of calibration specifications)
Figure
®
filter leaking or DiaSafe
®
filter leaking or DiaSafe
Fresenius 2008K Troubleshooting Guide
P/N 507298 Rev. B (Draft 1)
4A,
®
filter test valve leaking internally
®
filter test valve leaking internally
Section 10 – Pressure Tests Failing
Page 201