Hydac SK280-0.5/3218U-280ACF-VB-05 Piston Accumulator

A light 0.5 litre piston accumulator for 280 bar mobile and industrial hydraulics

The Hydac SK280-0.5/3218U-280ACF-VB-05 (HYDAC part number 3325242) is a piston accumulator from the weight-optimised SK280 series. A piston separates the oil from the nitrogen gas, which allows a higher pressure ratio and higher flow rates than a bladder, and the non-repairable construction keeps the series economical. This code is the 0.5 litre size, 335 mm long with a 60 mm outer diameter, weighing 3.1 kg.

The catalogue marks the series with PED/Europe pressure code certification. The gas side has HYDAC gas valve version 1 with an integrated M28x1.5 male thread, so it is rechargeable.

Technical specifications

What the code tells you

SK 280 – 0.5 / 3218 U – 280 ACF – VB – 05: SK280 is the series (4000 psi, non-repairable), 0.5 the size in litres, 3218 the material and piston combination (3 is the general-duty piston, followed by the piston, cylinder and seal materials 2, 1 and 8 for PUR), U the PED/CE country code, 280 the working pressure in bar, ACF the fluid connection, VB the gas valve and 05 the 50 mm piston diameter. For the SK280 series, the datasheet states that only the material combinations 3218 and 3268 are available.

Piston versus bladder

Piston accumulators suit applications needing high pressure ratios, large oil volumes or high flow rates. They need cleaner fluid, with filtration of 10 micron absolute (ISO 17/15/12) given in the datasheet, and a maximum continuous piston velocity of 3 ft/s for the general-duty type. They are used mainly for energy storage, with shock absorption only some of the time. The SK280 range comes in sizes from 0.16 to 10 litres, with 0.5 litre versions available in more than one piston diameter.

Check the hydraulic fluid for water content, because the PUR seal is not resistant to water, and keep the cleanliness at the filtration level named in the datasheet. Precharge only with dry nitrogen, with the fluid side depressurised. The datasheet lists mobile hydraulics and weight-sensitive industrial hydraulics as the series applications, and quick delivery for models with the standard connection, so ask the supplier which combinations are standard before choosing a special one.

A 0.5 litre piston accumulator is often used as a pulsation damper, a small energy reserve or a leakage make-up source on a compact circuit. State the minimum and maximum system pressure and the precharge you expect, so the supplier can check that the size is suitable.

Documents and quotation

The piston accumulator catalogue section is attached. Please state the precharge pressure and fluid. See also our hydraulic valves and components category.

How the SK280-0.5/3218U-280ACF-VB-05 works

A piston accumulator consists of a fluid section and a gas section, with a lightweight piston acting as a gas-proof barrier between them. In the SK280-0.5/3218U-280ACF-VB-05 the gas section is precharged with dry nitrogen through the gas valve. When the system pressure rises above the precharge, oil enters the fluid end and pushes the piston towards the gas end, compressing the nitrogen. When the system pressure falls, the gas expands and drives the piston back, returning oil to the circuit.

HYDAC piston accumulators are built from a cylinder with a finely finished internal surface, an end cap on the gas side and one on the fluid side sealed with O-rings, a lightweight piston and a sealing system chosen for the application. HYDAC lists their advantages as high ratios between precharge and maximum working pressure, high flow rates, gas-proof and leak-free operation, no sudden discharge of gas when the seal is worn, and space efficiency.

SK280 series: 50 mm bore sizes

The SK280 is the weight-optimised, non-repairable piston series, rated 4000 psi (280 bar). The datasheet gives these sizes for the 50 mm piston diameter (code 05), with an outer diameter of 60 mm:

A 0.5 litre size is also listed with the 60 mm and 80 mm piston diameters, which are shorter and heavier. Dimensions are for general information only.

SK280-0.5/3218U-280ACF-VB-05 selection & ordering guide

• Material and piston (3218): 3 = general duty piston; 2 = machined carbon steel piston; 1 = machined carbon steel cylinder and end caps; 8 = PUR seals (−22 to 180 °F). For the SK280 only the combinations 3218 and 3268 (FPM seals) are available.
• Country of installation: U = PED/CE; S = USA and S1 = Canada CRN are other codes.
• Fluid port (ACF): A = female thread, C = SAE (ANSI B1.1), F = SAE-8, 3/4-16 UNF.
• Gas side (VB): refillable gas valve with M28 × 1.5 thread. A factory-precharged, sealed (000) version exists for the SK280 only, with a minimum order quantity of 200.
• Seal compatibility: PUR is resistant to mineral oils HL and HLP and HFA fluids, but not to water, water-glycol, alkalis or acids. FPM suits HFD fluids and hydrocarbons.

Our team can help confirm the correct ordering code for your fluid and pressure range.

Installation & maintenance

• HYDAC piston accumulators may operate in any position; vertical installation with the gas side up is preferred.
• Use HYDAC mounting components to minimise the risk of failure from vibration.
• Keep the fluid clean: the datasheet gives filtration of 10 µm absolute (ISO 17/15/12) for its piston types.
• Precharge with dry nitrogen only and check it regularly with the fluid side depressurised.
• Because the SK280 is non-repairable, the unit is replaced rather than resealed at the end of its life.

Typical applications in Oman & the GCC

HYDAC names mobile hydraulics and weight-sensitive industrial hydraulics as the applications of the SK280 series. In Oman and the GCC, a 0.5 litre piston accumulator fits compact mobile machines, cranes, vehicle hydraulics and small power units where space and weight are limited and a high pressure ratio is needed.

Why source from Seven Star LLC

Seven Star LLC supplies HYDAC piston accumulators, charging equipment and mounting clamps across Oman and the GCC. Request a quote for the SK280-0.5/3218U-280ACF-VB-05 with your precharge pressure and fluid.