EN
AR
CS
DA
NL
FI
FR
DE
EL
IT
JA
KO
NO
PL
PT
RO
RU
ES
SV
TL
IW
ID
LV
SR
SK
VI
HU
MT
TH
TR
FA
MS
GA
CY
IS
KA
UR
LA
TA
MY
Control valve seal leaks behave differently from percussion bore leaks — they show up in the wrong place at the wrong time. A percussion bore leak appears during drilling, under load. A control valve seal leak typically appears at idle, or during the fraction-of-a-second transition between percussion and rotation, because that's when the valve spool moves through the position where the worn seal sits. That timing pattern — leak at spool transition, not during steady percussion — is the diagnostic key that most maintenance manuals skip.
The physical location of the bypass matters too. Worn control valve seals leak internally — oil crosses from the high-pressure port to the return port without doing any work. The external oil level drops 1.5–3 L per 8-hour shift without visible external leakage, and the system runs hotter than normal because the bypassed oil throttles through the worn seal gap, converting 12–18 bar of pressure differential to heat. A drifter running 6°C hotter than its circuit partners on the same jumbo, with matching oil levels dropping faster, has a control valve seal problem until proven otherwise.
Control Valve Seal Diagnosis Sequence
|
Test Step |
Method |
Expected Result (Healthy) |
Indication of Seal Failure |
|
Step 1: Isolate circuit |
Block percussion circuit; run rotation only at full pressure |
No oil loss, stable pressure at rotation gauge |
Pressure drop or oil loss during rotation only = rotation valve seal suspect |
|
Step 2: Pressure-hold test |
Pressurize percussion circuit to 175 bar; kill pump; observe for 60 seconds |
Pressure holds within 3 bar over 60 seconds |
Drop exceeding 8 bar in 60 seconds = internal bypass confirmed |
|
Step 3: Spool position test |
Slowly cycle valve spool by hand while pressurized (low pressure, 40 bar) |
Smooth spool movement, no oil weeping at any position |
Oil weep at specific spool position locates worn seal land |
|
Step 4: Oil temperature mapping |
Compare return temperatures from each circuit on multi-boom machine |
Circuits within 4°C of each other under same load |
One circuit 8°C+ hotter = internal bypass on that circuit's control valve |
|
Step 5: Flow meter check |
Measure pump output vs measured circuit flow at percussion inlet |
Flow differential below 3 L/min |
Differential above 7 L/min confirms internal bypass volume |
Internal bypass wastes 8–15% of pump output per failed seal, burning fuel to generate heat rather than percussion energy. On a three-boom jumbo running three shifts, that inefficiency compounds into measurable energy cost within a week. HOVOO supplies control valve seal sets for DD2710 and DT1131 jumbos with spool-clearance measurement data. Full specifications at hovooseal.com.
