HCYY11112005 Main Boom Angle Cylinder for Aerial Work Vehicles

Extend Side — Full Bore Area

The full bore area of the Φ55 piston is 2,376 mm². At 21 MPa, this produces approximately 49.9 kN of extension force — sufficient to push the main boom upward through its elevation arc. This is the primary working stroke: raising the boom from stowed to operating angle.

Retract Side — Minimal Annular Area

The annular area (bore minus rod) is only 412 mm² — just 17% of the full bore area. At 21 MPa, the retract force is approximately 8.7 kN. This small retract force is acceptable because boom lowering is gravity-assisted: the boom's own weight drives the descent, and the cylinder's retract circuit primarily controls the descent speed through metering rather than providing pulling force.

HCYY11112005 — This Product

Φ55×Φ50×506, 21 MPa working / 26.5 MPa max, 1259.7 mm installation distance, 32 kg. Extreme 0.91 rod-to-bore ratio for column-load applications on specific AWV platforms.

HCYY11112010 — Variant

A different main boom angle cylinder for a different AWV platform — different bore, rod, stroke, and mounting dimensions. Not interchangeable with the HCYY11112005. Always verify the part number on the cylinder you are replacing.

Why is the rod-to-bore ratio 0.91 — doesn't that leave almost no retract force?

The annular area (Φ55 bore minus Φ50 rod) is only 412 mm², producing approximately 8.7 kN of retract force at 21 MPa. This is intentionally low. The main boom angle cylinder does not need to actively pull the boom down — gravity does that work. The retract circuit primarily controls the descent speed by metering the oil flow back to the tank. The engineering priority is the rod's second moment of area (resistance to buckling), which increases with the fourth power of diameter. The Φ50 rod provides the structural rigidity needed to hold the boom at working elevation as a loaded column.

The boom lowers faster than it rises — is this the cylinder or the valve?

The asymmetric speed is normal for this main boom angle cylinder and is a direct consequence of the 0.91 rod-to-bore ratio. At the same pump flow rate, the retract stroke moves approximately 5.8× faster than the extend stroke because the same volume of oil fills a much smaller annular area. Combined with gravity assistance during boom lowering, the descent is noticeably faster than the ascent. This is a designed characteristic. However, if the descent speed has increased compared to when the machine was newer, the counterbalance valve may need adjustment, or the cylinder may have developed internal seal bypass.

Can I use a standard Φ55 cylinder with a Φ35 rod as a replacement?

No. A Φ35 rod (standard ratio 0.64) would have inadequate buckling resistance for the column loading this main boom angle cylinder sustains. The Φ50 rod has approximately 4.2× the second moment of area of a Φ35 rod — directly translating to 4.2× the critical buckling load. Using a thinner rod risks catastrophic rod buckling under sustained boom-hold loading, which could cause uncontrolled boom descent with personnel on the platform. Always match the exact bore and rod specification: Φ55×Φ50.

Why is the maximum withstand pressure 26.5 MPa rather than the typical 1.5× (31.5 MPa)?

The 26.5 MPa max withstand pressure represents a 1.26× ratio over the 21 MPa working pressure. The exact test ratio is determined by the AWV platform manufacturer's design specification — not all aerial work vehicles use the standard 1.5× ratio. The oversized Φ50 rod provides additional structural margin that partially compensates for the lower proof ratio, as the rod itself absorbs a significant portion of the compressive load independently of the hydraulic pressure. Every HCYY11112005 is proof-tested at 26.5 MPa before shipment. Contact Korea Ever-Power for a replacement quotation.

Replaced the main boom angle cylinder on our AWV — the original had developed internal bypass that caused the boom to slowly settle under load. The Φ50 rod on this HCYY11112005 is noticeably thicker than what I'd expect on a Φ55 bore cylinder — when I first saw it I thought it was the wrong part. But the specs matched perfectly: Φ55×Φ50×506, 1259.7 mm pin centres, everything aligned. Boom now holds steady at any angle with zero drift during our 30-minute hold test. Excellent product.

We ordered the HCYY11112005 (boom angle) together with the HCYY11112003 (lifting) and HCYY11112004 (steering) for a complete AWV cylinder overhaul. All three arrived in one shipment, individually packaged with test certificates showing the correct proof pressures — 26.5 MPa for the boom angle, 27 MPa for the lifting, 30 MPa for the steering. Our technician installed all three in one day. The machine is back in service and performing at OEM standard. Total cost for all three was roughly 45% of the OEM channel quote for just the boom angle cylinder.

Cylinder works well, correct dimensions. The installation was more challenging than expected — at 32 kg and 1,259 mm long (retracted), it's awkward to manoeuvre into the turntable space without a second pair of hands. The pin alignment at both ends took some patience. Once installed, the boom angle control is smooth and precise. The boom descends noticeably faster than it rises — I initially thought this was a fault, but I understand now it's the design of the Φ50 rod annular area. Four stars for the difficult installation, not for the cylinder quality.

Second main boom angle cylinder we've purchased from Ever-Power. Same quality as the first. The Φ50 rod chrome is flawless — critical because this rod is under compression for hours at a time when the boom is holding position. Any surface defect that initiates a corrosion site would compromise the structural integrity. Delivery was 22 days to Brazil. No complaints. Will order again when the next AWV in our fleet reaches its service interval.