Hydraulic piston seals, also known as piston seals, piston packings or piston rings, separate the pressure side from the non-pressure side in a cylinder. They are installed on the piston and run along the cylinder bore. This allows the cylinder to generate force in both directions. Unlike with a rod seal, leakage is not visible on the outside. Oil flows past the piston from one chamber to the other, causing the cylinder to drift under load or lose force.
This is precisely why hydraulic piston seals are often replaced too late. Techniparts supplies every brand and every size, metric and inch, for low and high pressure. If we do not have a size in stock, we will provide a technically equivalent alternative.
A hydraulic piston seal is installed on the moving piston inside a hydraulic cylinder. The seal runs along the inside of the cylinder bore and helps prevent oil from flowing unintentionally from one pressure chamber to the other.
In a double-acting cylinder, the pressure changes sides during each stroke. The piston seal must maintain the pressure difference between both chambers so that the cylinder can move in a controlled manner and deliver the required force.
Unlike leakage at a rod seal, leakage past the piston is usually not visible on the outside. The hydraulic fluid remains inside the cylinder but flows internally past the piston. As a result, a cylinder may lose force or slowly drift under load.
When hydraulic fluid under pressure is supplied to one side of the piston, a force is generated that moves the piston and piston rod. The piston seal prevents internal leakage and therefore helps maintain the pressure difference across the piston.
The sealing profile must make sufficient contact with the cylinder wall while still being able to move smoothly. Excessive friction can cause wear and stick-slip, while insufficient contact pressure can result in internal leakage.
At high hydraulic pressure, soft sealing material can be forced into the clearance gap between the piston and cylinder wall. This is known as extrusion. Depending on the profile and pressure, backup rings or anti-extrusion rings can therefore be used.
When selecting a hydraulic piston seal, it must first be determined whether the seal needs to withstand pressure from one or both directions.
A single-acting piston seal is designed to seal pressure from one direction. This version is used, for example, in cylinders that are hydraulically driven in one direction and return through gravity, a spring or an external load.
In a double-acting hydraulic cylinder, the pressure changes sides during each stroke. This requires a seal that can function in both directions or a sealing arrangement that seals both pressure directions separately.
Hydraulic piston seals are available in different profiles and designs. The appropriate type depends on factors including pressure, speed, movement, available installation space and the required friction characteristics.
A U-cup is a commonly used sealing profile in which the pressure helps press the sealing lip against the sealing surface. Many versions are single-acting.
Compact seals combine several functions within a single sealing set. They can consist of a central sealing element with backup and guiding elements and are widely used in mobile hydraulics.
A PTFE slide ring seal generally consists of a PTFE sealing element preloaded by an elastomer O-ring. This design provides low friction and can be suitable for double-acting applications.
For heavy-duty industrial applications, chevron packings or stacked seal sets can be used. These consist of multiple sealing elements and are used, among other applications, in older or heavily loaded hydraulic systems.
The material of a hydraulic piston seal largely determines its pressure resistance, wear resistance, temperature resistance, friction and chemical resistance.
PU is a widely used material for hydraulic piston seals. It combines high wear resistance with good mechanical properties and is suitable for many high-pressure applications.
NBR is used with many mineral hydraulic oils and offers a favourable combination of sealing properties and price. The exact load capacity depends on the compound and profile.
FKM/FPM can be used at higher temperatures and under various chemically demanding conditions. Compared with standard NBR, HNBR offers improved temperature and ageing resistance, among other properties.
PTFE offers low friction and broad chemical resistance. PTFE is widely used in slide ring seals and can be beneficial when stick-slip needs to be limited.
EPDM can be suitable for certain applications involving water, steam or specific hydraulic fluids. The material is not suitable for many mineral oils. Therefore, always check the compatibility between the material and the medium.
| Material | Indicative temperature range | Strengths | Points to consider |
|---|---|---|---|
| Polyurethane (PU) | -30 to +110 °C | Standard in hydraulics, high pressure and wear resistance | Not resistant to hot water and steam |
| NBR | -30 to +100 °C | Lower pressures, favourable price | Limited wear resistance |
| FKM (Viton) | -20 to +200 °C | High oil temperatures and aggressive media | Higher cost |
| HNBR | -30 to +150 °C | Higher temperatures than NBR, good strength | More expensive than NBR |
| EPDM | -45 to +150 °C | Water, steam and brake fluid | Not resistant to mineral oil |
| PTFE (Teflon) | Wide range of applications, low friction, no stick-slip, both directions |
To select the correct hydraulic piston seal, at least the operating pressure, speed, temperature and hydraulic fluid must be known.
At higher pressures, the risk of extrusion of the sealing material increases. The clearance between the piston and cylinder wall, material hardness and any backup rings must therefore be assessed together.
At low speeds and with frequent start-stop movements, stick-slip can become a problem. Low-friction profiles, such as certain PTFE versions, can offer advantages in these applications.
Not every seal is suitable for every hydraulic fluid. With biodegradable oil, water-glycol, synthetic fluids or other special media, the material resistance must be checked in advance.
At high pressure, backup rings or anti-extrusion rings can be used to provide additional support for a hydraulic piston seal. These harder rings are positioned on the side of the sealing clearance.
The backup ring helps prevent the softer sealing material from being forced into the space between the piston and cylinder wall. This can reduce damage to the sealing edge.
Also view the available backup rings and anti-extrusion rings for applications where protection against extrusion is required.
A hydraulic piston seal works together with the guidance of the piston. Guide rings and guide strips absorb lateral forces and help prevent the piston from running directly against the cylinder wall.
When the guiding components are worn, the piston can become misaligned. This places a greater load on one side of the piston seal and can cause accelerated wear.
Therefore, during a cylinder overhaul, also inspect the hydraulic guide rings and hydraulic guide strips.
A defective piston seal usually causes internal leakage. As a result, it is not always immediately visible from the outside of the cylinder that there is a problem.
When hydraulic oil flows past the piston from one chamber to the other, the cylinder can no longer maintain its position properly. A cylinder that slowly drifts while under load can therefore indicate internal leakage.
Internal leakage reduces the effective pressure difference across the piston. As a result, the cylinder may deliver less force or respond more slowly.
Cylinder drift is not caused exclusively by the piston seal. Also check valves, pipework, the cylinder wall and other possible internal leakage points before dismantling the cylinder.
A piston seal and rod seal are both used inside a hydraulic cylinder, but they have different positions and functions.
The piston seal is installed on the moving piston and separates the different pressure chambers inside the cylinder.
A hydraulic rod seal is installed in the cylinder head and helps prevent hydraulic fluid from leaking out along the moving piston rod.
Hydraulic piston seals are used in hydraulic cylinders in a wide variety of mobile and industrial machinery.
Excavators, cranes, aerial work platforms and other construction machinery use hydraulic cylinders for lifting, tilting and moving heavy loads.
Piston seals are also used in tractors, agricultural machinery and telescopic cylinders under a wide range of pressure and environmental conditions.
Hydraulic piston seals are also used in presses, material-handling machinery, marine applications and industrial production machinery.
Techniparts supplies hydraulic piston seals from a wide range of manufacturers. Existing seals can often be identified by their type number, profile, dimensions and material.
This makes it possible to find an original type or a technically equivalent alternative for many existing cylinders, even when a particular type number is no longer available as standard.
| Brand | Types | Material |
|---|---|---|
| FREUDENBERG SEALING TECHNOLOGIES | OMK-MR, OMK E OMEGAT, OMK-S, OMK ES OMEGAT, T18, L43, T20, T22, TM21, TMP 21, NA 300, L26, SIMKO 300, NA 150, NA 250, NA 400, T42, T44, 0215, 0217, OMK PU, SIMKO 320 X2, SIMKO 520, L27, T19, TFMA, TDUO, TDUOH, T MET VEER, T ZONDER VEER, STAPELSET EK, STAPELSET EKV, FOA, NAP 210, NAP 300, NAP 310, NAPN, KDN, NADUOP, AIRZET PK, PNEUKO G, PNEUCO M 210, PNEUCO M 310, TDUO-P | PU, Polyurethane, PTFE, NBR, Viton, HNBR, 95auv149, 95auv925, 95 auv 149, 95 auv 925, Disogrin |
| DICHTOMATIK | KDS 01, K01, KK 03, K03, KK22, K22, KK25, K25, KK71, KN 05, S05, KN 21, MA21, KN 25, MA 25, KN 36, MA 36, KNA 16, K16, KNA 23, MA 23, KNA 28, MA 24, KNA 44, MA 44, KPOR 30, K30, KPOR 31, K31, KPUOR 70 | NBR Rubber 90 30 06 (903006), EPDM, PUR TPU 95 34 01 (953401), Polyurethane, PTFE, Teflon bronze graphite, blue, black |
| ANGST EN PFISTER | Lubroseal, LDEMP, LT19P, L9490P, LSIM300P, L300P, LT18P, LL43P, LG18P, LOMKP, LEKP, LL27P | Nitrile NBR, PUR AU, Teflon PTFE |
| BALSEAL | Seal Series | UHMW PE, PTFE Glass MOS, Fiber Carbon, TA, G, GC, GFP, GFPM, GL, SP, UPC, FDA |
| CLARON | SPS, DP, DPE, DPW L, JS-H, DPDS, SFD, PRF, PFD, SPW, CSPG, CS-8, CSPGI, CS-5, 841, CS2, CS4, D-Ring, DSE, CP, P, GP, PRU, PFU, CPE, PEO, GPE, PW L, GPW, CPU, FPC, PRC, 851, PDE, PSR, GP | Nitrile, NBR 70 Shore, NBR 90 Shore, AU, Polyurethane |
| DLI | MDD/IDD-P, MDD/IDD-EO, MDD/IDD-W, MDD/IDD-PLW, MDL, MDB-W, MDB-EO, MHM/IHM-W, MHM/IHM-EO, IOP, MSP/ISP, MDP/IDP, MSK | NBR, TPU, Polyester, Acetal |
| ERIKS | 9000, 2001, 0018, 0011, DVSV, 0820, 0850, 0410, OMNISEAL, 0043, 0026, EZM, PNBR | NBR, Viton, FKM, FPM, EPDM, PU, AU, Polyurethane, Brass, Stainless Steel, PTFE |
| EVCO | 210, 270, GT3, GRC, PDE, PDP, PST, TPM, TTO, TTW | PTFE, PU Polyurethane, AU, NBR |
| GUARNITEC | TPM, TPM/E, TPL, TPS, TDE, TPD, PDE, PDH, PDP, TGU, GT3, TRU, TTU, TTE, TTE/W, TUT, TTO, TTQ, TTD, TTW, GUA RING 01, GUA GER | AU, PU, NBR, Rubber Metal |
| HALLITE | 50, 51, 52, 53, 54, 56, 58, 64, 65, 68, 77, 714, 730, 735, 753, 754, 755, 764, 770, 775, 780 | NBR, Polyurethane, PUR, Polyester, PTFE, Teflon, Red, Blue, Black |
| HECKER GSM | PKS, PKS1, PKK, PKK1, EUK1-P, UNA-P, EUK, DK4 W, DK4 WB, DK4 WS, EUK1-H, MN1, MA1-4, UNX1, UNX2, UNA, UNA1, UNA2, UNA3, UNX7, UR, UG1, UG2 | Rubber, Fabric, NBR, PTFE, PU, AU, GI |
| HUNGER | GD1000, GD1000K, GD200P, TDA, TDMA, GGDA, ZSDA, GODA SP, GODA SPE, GDSA | NBR, PU, PTFE, POM, PA 6, PA-CF, UHMW PE, PEEK, Hytrel, MVQ, FPM, FMVQ |
| JAMES WALKER | Chevron, Solosele, Twinset, U-rings, Lofilm HD | Rubber / Canvas, NBR, Viton, Polyurethane, PU |
| KACO | PNAP, PNZP, QTMF, PTMP | NBR, ACM, VMQ, FKM, FPM |
| KASTAS | K, 03, 15, 16, 17, 18, 19, 20, 23, 26, 40, 41, 42, 43, 25, 50, 54, 55, 57, 58, 59, 62, 63, 751, 753, K03, K15, K16, K17, K18, K19, K20, K23, K26, K40, K41, K42, K43, K751, K753, K50, K54, K55, K57, K58, K59, K62, K63 | PU, NBR, Steel, Polyurethane |
| NORDEX | Wynseal, PUA, APDE, APDS, APMP | PU, Polyurethane, AU |
| PARKER (PRÄDIFA) | B7, C2, CP, D1, DK, DL, DP, DE, E4, EK, GD, KR, KU, M4, NG, N0, NO, OA, OE, OG, OK, PZ, Z5, Z7, Z8, ZC, ZP, ZQ, ZS, ZW, ZX, AK, OK (double), T Seal | NBR, Polyurethane, Viton, HNBR, PTFE, FKM, FPM, Black, Brown, Green, P5008, P5009, P6000, P5004, P5000, P5001, P5062, P5075, P5007, P5070, P5011, P5080, P5010, P5012, P4300, P5500, N3571, N3570, N3578, N3580, N3584, N3582, E3676, E8536, E8608, V3664, V3656, V3638, V3681 |
| POLILAS | PK, PK1, PK3, PK4, PPN, OM, OMB, OMS, OMT, PB, PB2, PN, PN10, PN11, Chevron set | NBR, AU, PU, Polyurethane |
| POLYPAC / SSI SEALTECH | B NWO KR, CH, CH/NEO, CH3, D11W H, 10, DAS, DBM, DC, DDE, DDEM P, DPC, DPS, DSM, DS/NEO, DO, E/GR A B, EUD N P, GPK, GPS, GPP, MU, PHD, RSE AE W AR, TDO, TDO-P, VOP, VVP, PHD/P, DBM, EUD, DPS/DPV, SELEMASTER DSM | NBR, HNBR, MVQ, FPM, EPDM, Viton, PTFE, PT01, PT, Polyurethane, PUR, AU, HDPE, PA, PF, PBTP, PU02, PU05, PU08, PU10, PU12, PU14, PU20, PU21, PU22, PU23, PU25, PU26, PU27, PU30, PU40, White, Green, Black, Brown |
| SKF ECONOMOS SEAL JET | CUT, PEN, GHT, GH, GL, URG, M, MD, M-R, A, MSS, SAAR, SAW, SA, SWRR | Ecopur, H, G, T, X, S, XH, XS, TPU, CPU, NBR, HNBR, Green, Red, Blue, Black, Grey |
| TRELLEBORG SEALING SOLUTIONS | Turcon: Stepseal 2K, VL-seal, Glydring, Glydring T, AQ-Seal, AQ5-Seal, Double-Delta, Variseal M2, Zurcon: U-Cup PUA, Wynseal, DAS seal, Polypac: PHD/P, DBM, EUD, DPS/DPV, Selemaster DSM | PTFE / TEFLON (TURCON): T01, T05, T10, T12, T16, T19, T24, T25, T29, T40, T42, T46, T47, T51, T52, T59, T78, T99, M12, Q2J, MO2, M83, PUR (ZURCON): Z201, UHMWPE (ZURCON): Z20, Z22, Z24, Z43, Z431, Z48, Z51, Z52, Z80, Elastomer: NBR, FKM, HNBR, EPDM, FFKM |
For older machines, inch sizes and special cylinders, hydraulic piston seals can be manufactured to size. Where possible, provide the cylinder bore, groove diameter, groove width, pressure, temperature, medium and required material.
When overhauling a cylinder, it is advisable to inspect the other sealing and guiding elements in addition to the piston seal.
View our hydraulic rod seals for sealing around the moving piston rod.
Hydraulic wipers can be used to protect the cylinder against dirt and contamination.
Hydraulic guide rings and hydraulic guide strips are also available for supporting and guiding the moving components.
A hydraulic piston seal is installed on the piston of a hydraulic cylinder and helps prevent hydraulic fluid from flowing internally between the different pressure chambers.
One possible cause is internal leakage past a worn piston seal. However, also check valves and other components of the hydraulic system.
Both versions are available. In double-acting hydraulic cylinders, a double-acting sealing function is often required because the pressure changes sides during the stroke.
A backup ring or anti-extrusion ring helps prevent soft sealing material from being forced into the clearance between the piston and cylinder wall at high pressure.
Common materials include PU, NBR, FKM, HNBR, PTFE and EPDM. The correct choice depends on pressure, temperature, speed and hydraulic fluid.
Important dimensions are the outside diameter (D), inside diameter (d) and groove width (L). If the old seal is deformed, preferably measure the cylinder bore and groove directly.
The piston seal separates the pressure chambers inside the cylinder. A hydraulic rod seal prevents oil from leaking out along the piston rod.
Yes. For older cylinders, inch sizes and non-standard grooves, custom-made hydraulic piston seals or technically suitable alternatives can be supplied.
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