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GENERAL TROUBLESHOOTING Type A/H Panel Operation And Troubleshooting Hydraulic Brake Systems   Industrial Brake Products   AH-ARC, AH-ERC, and AH-HRC Panel Operation for Air-Over-Hydraulic Brake Systems
The AH panels have the following common components (as illustrated in panel piping diagrams):
Air storage tank(s) Protected air storage tank Starter with controls for compressor Pressure switches Pressure cluster(s) Moisture ejection valve Relay Emergency Valve (REV)
The relay emergency valve is the heart of the panel operation. Understanding this valve function will assist in understanding the AH panel operation.
This valve controls pressure to the service brake pressure cluster. It applies pressure from the right half of the horizontal reservoir. Whenever emergency port E is pressurized above 50 psi, reservoir port R pressure is poised for application to delivery port D at whatever pressure is applied to service port S. Without pressure at the service port, no pressure is applied to the delivery port.       Whenever emergency port pressure drops below 40 psi, pressure at the reservoir port is applied to the delivery port. Hence the valve applies pressure to the service brake pressure cluster in "emergencies," although a tiny "bleed-down bypass" bleeds delivery port pressure through the service port. After several hours the "emergency" brake pressure is fully released.

Panel Operation Summary
AH-ARC Normal Service Braking	Air is delivered to the service port on relay emergency valve (REV) via air treadle valve located in operator's cab. Applying pressure to service port meters air to the pressure clusters, which forces hydraulic fluid to the brake(s).
AH-ERC Normal Service Braking	Air is delivered to service port on relay emergency valve (REV) by opening (energizing) the service solenoid valve (SSV). REV valve meters air to the pressure cluster(s), which forces hydraulic fluid to the brake(s).
AH-HRC Normal Service Braking	Depressing foot pedal on control cylinder in operator's cab delivers hydraulic pressure to hydraulically controlled air valve. Air is metered through a check valve to pressure cluster(s), which forces hydraulic fluid to the brake.
NOTE:  In all cases, for normal service braking, 50 psi of air pressure must be present at the emergency port on the relay emergency valve (REV).
	For AH-ARC panels, air is piped through a one-way check valve from the storage tank. For AH-ERC and AH-HRC panels, air is piped from the storage tank but through a normally closed solenoid. The solenoid (emergency solenoid valve) must be held open (energized) so air is delivered to the emergency port.

Emergency Braking	Whenever emergency port pressure drops below 40 psi on the REV, air from the protected tank will be delivered to the pressure cluster(s), which forces hydraulic fluid to the brake.
NOTE:  Emergency braking can occur when:
	Loss of air pressure or low air pressure Loss of power (AH-ERC, AH-HRC) PS2 pressure switch opens (AH-ERC, AH-HRC) Closing emergency solenoid valve (de-energized) by contact control. This is commonly referred to as the second step of braking for AH-ERC panels.
1PS Pressure Switch (J078061)	Turns compressor on/off.
2PS Pressure Switch (J078061)	AH-ARC panel sounds low pressure alarm. Emergency braking occurs as noted above for AH-ERC and AH-HRC systems.
BPB Bleeder Push Button (J010068)	Opens bleeder(s) by energizing solenoid on fluid reservoir bleeder.
MPR-Motor Protection Relay	On AH-ERC/AH-HRC panels, relay provides contact for customer use as motor protection.
BFP-Brake Filling Pushbutton	Strokes pressure cluster for bleeding hydraulic lines.
Moisture Ejection Valve	Each brake application causes a small amount of air to expel accumulated moisture in storage tank.

 

Troubleshooting Hints
PROBLEM	POSSIBLE SOLUTION
Brake does not actuate	Observe pressure cluster to determine if unit "stroked forward." An 8 x 1 cluster has an indicating rod, a 5 x 1 cluster has a rubber boot that moves. If cluster strokes, panel may be operating and problem is at brake. Relay emergency valve not functioning. No power or no air pressure. Solenoid valve not functioning.
Brake stays set	No air on emergency port of REV so brake is actuated.
Brake "spongy"	Air trapped in hydraulic lines; system needs to be bled.
Bleeding Procedure
Open fluid reservoir bleeder (BPB) by depressing push button (and holding in).   Stroke pressure cluster forward by doing one of the following, depending on panel: AH-ARC - depress bleeding control valve or treadle valve. AH-ARC - depress BFP brake filling push button. AH-HRC - depress bleeding control valve or control cylinder.   Release push button (BPB).   Retract pressure cluster by releasing step 2. This procedure will have to be repeated many times to completely bleed the system. Fluid travel is only five to seven feet. Refill reservoir(s) frequently during bleeding.   If the pressure cluster stroke is reduced to a travel of about 1-1/2", this may be an indication that the system is bled.