A Denison T6 or T7 vane pump that is noisy, will not make pressure or is leaking at the shaft is usually telling you about its inlet, its air bleed or its oil, not about a worn-out cartridge: Denison's own vane troubleshooting guide puts 80% of failures down to fluid contamination, and its symptom tables keep coming back to rotation, air and suction. Rotation can be changed on these pumps, and Parker publishes the procedure: on a cartridge with bi-rotational port plates you flip the cam ring and move the dowel pin, and on one with uni-rotational port plates you change the port plates as well.
This page works through Denison's symptom tables in the order the factory gives them, explains what is actually different between a T6 and a T7, and covers the rotation change and a short note on Gold Cup piston pumps that will not stroke.
Denison's own numbers on why these pumps fail. The factory guide (1-EN0721-A) says failures in the first 500 hours of service are premature failures, caused by ignoring instructions or application limits, and that 80% of failures are linked to fluid contamination: air, dirt, water and wrong viscosity. The pump is hydraulically balanced, so the ball bearing carries no internal load. When one of these pumps dies young, look at the system before you blame the pump.
Why is my Denison T6 or T7 vane pump noisy?
Air. Either air drawn in with the oil (aeration) or vapor pulled out of the oil by a starved inlet (cavitation). Denison describes the difference this way:
- Aeration is air getting into the oil: low reservoir level, a small or turbulent tank, a suction leak, a return line dumping above the oil, or water turning to steam. The vanes lose their balance, wear grooves in the port plates starting in the discharge area, and the first thing you notice is the noise. Severe aeration can break a vane.
- Cavitation is the inlet pulling a vacuum. Gas dissolved in the oil (Denison puts it at 6 to 7%) comes out of solution at roughly -0.2 bar, the oil turns cloudy, and the bubbles collapse on the metal under pressure and erode it. Denison's example: 100 liters of oil foamed by cavitation takes about 4 hours to go clear again. The noise is much louder than normal and gets louder as pressure rises.
Denison's noise checklist, in its order, rewritten for the shop:
| Where the noise comes from | What to check |
|---|---|
| The pump | Shaft alignment and coupling balance, key properly fastened, air bleed done, no air leak between tank and pump (including past the shaft seal), hose strain on the pump, oil level, aerated oil in the tank, clogged or undersized strainer, inlet pipe below the oil level, clogged or small breather, speed and oil within catalog limits, inlet pressure not higher than outlet pressure. |
| The surroundings | Noise carried back through hoses, pressure piping length amplifying it, a tank structure that resonates, the electric motor fan or balance, the cooler, and a filter running on its open bypass valve. |
Two more causes from Denison's mechanical failure section that we see on the bench: on the mobile T6 (the M versions) a hollow pin-vane holdout fitted upside down makes the pump noisy, and a cartridge put back together without checking that the rotor turns free can have vanes tilted and squeezed between the port plates, giving noise, limited pressure and unsteady flow. The two cartridge screws only hold the pieces together. Denison says to tighten them lightly and always check that the rotor and vanes turn freely after reassembly.
More on the sound itself in hydraulic pump making noise: whining and cavitation.
What inlet pressure, oil and cleanliness limits does a Denison T6 or T7 need?
These come from Parker's overall instructions for the T7, T67 and T6 single pumps (HY29-0035). Check your installation against them before you open the pump.
| Item | Factory figure |
|---|---|
| Minimum inlet pressure | Never below 0.8 bar absolute (-0.2 bar gauge), 11.6 psia (-2.9 psig). The minimum rises with displacement and speed, so check the sales leaflet chart for your size. |
| Maximum inlet pressure | Standard shaft seals are limited to 0.7 bar (10 psig). Some seals allow 7 bar (100 psig). |
| Inlet to outlet difference | At least 1.5 bar (22 psi) between inlet and outlet at all times. |
| Oil velocity | Inlet 0.5 to 1.9 m/s (1.64 to 6.23 ft/s); return under 6 m/s (19.7 ft/s). Denison's guide adds that below 0.5 m/s air stays trapped in the pump and inlet pipe. |
| Inlet strainer | Parker does not recommend one. If you must, nothing finer than 100 mesh (149 micron). |
| Breather | Sized at three times the maximum instant return flow. |
| Minimum speed | 600 rpm for industrial pumps, 400 rpm for mobile pumps (troubleshooting table). |
| Viscosity | Optimum 30 cSt (140 SUS). Maximum at full speed and pressure 108 cSt (500 SUS). Cold start maximum 860 cSt (3,900 SUS) industrial, 2,000 cSt (9,400 SUS) mobile. Minimum 10 cSt (60 SUS) on anti-wear petroleum oil (HF-0, HF-2), 18 cSt (90 SUS) on HF-1, HF-3, HF-4 and HF-5. |
| Cleanliness | NAS 1638 class 8 or ISO 19/17/14, or better. |
| Water | 0.10% maximum in mineral oil, 0.05% in synthetic, crankcase and biodegradable fluids. |
Denison's guide also makes a point about temperature that catches people out: a tank at 50°C (122°F) can mean up to 130°C (266°F) locally inside the pump, so viscosity worked out from tank temperature flatters the oil. See our oil viscosity guide by pump type and fluid cleanliness and flushing.
Why is my Denison vane pump not making pressure or flow?
Denison's table for "no flow, no pressure" asks eight questions in a fixed order. Work them top to bottom, because the first ones are free.
- Is the pump turning? Coupling turning, keys in both shafts, shaft not broken.
- Is it turning the right way? Compare the pump's rotation with the arrow on the nameplate, and check the electric motor wiring. R is clockwise and L is counterclockwise, viewed from the shaft end.
- Is the air bled off? Crack a fitting on the pressure line, with the circuit unloaded so pressure cannot rise, and tighten it once air-free oil appears. Parker says the pump should prime within a few seconds.
- How is the inlet? Inlet gate valve open, oil level up, suction pipe below the oil, no air leak (a missing inlet flange seal is a classic), pump not mounted too high above the oil, and the tank vented. A completely sealed tank will not let the pump prime.
- Is the oil too thick? Cold, heavy oil will not feed the inlet, and Denison notes that very high viscosity at low speed can leave vanes stuck in the rotor so the pump makes no flow at all.
- Is the flow going somewhere else? Relief valve set very low, a directional spool stuck in a position that dumps to tank, or a check valve fitted backwards.
- Is the motor or cylinder leaking it away? A worn motor or blown cylinder seals can swallow the whole flow.
- Is the speed high enough? 600 rpm minimum industrial, 400 rpm mobile.
For "not enough pressure," Denison adds two system questions: is the flow the circuit demands more than the pump delivers (then it cannot build pressure), and is something downstream leaking internally and holding pressure down. For "not enough flow" it adds displacement and speed checks, a half-open gate valve, a long or high inlet, a suction pipe end not cut on a bevel (Parker suggests at least 45°), a suction too close to the return or the tank bottom, missing baffles, and hot thin oil whose internal leakage "consumes" the flow.
Inside the pump, the guide lists a cartridge dowel pin not seated correctly in the housing as a cause of no pressure, unsteady flow, cavitation and noise. That is an assembly fault, and it is worth checking on any pump that came back from a rebuild and never worked right. For everything outside the pump, see hydraulic pump not building pressure.
Why does my Denison vane pump run hot?
Denison splits it in two. If the heat shows up with the pump running unloaded, look at the inlet and the tank: oil level, suction pipe length and size, air bleed, tank volume against flow, a cooler that is missing, undersized or shut off, a circuit that sends flow straight back to the pump inlet (a tiny closed loop that cannot shed heat), fluid quality and velocity, and a filter running on its bypass. If the heat only shows up under pressure, check viscosity, the pressure rating, the cooler, a relief valve that is always cracked open, another component with an internal defect, and the temperature difference between inlet and outlet. More in why is my hydraulic pump overheating.
Why is my Denison vane pump leaking at the shaft seal?
Denison asks first whether the seal is destroyed or just leaking.
| Condition | Denison's checks |
|---|---|
| Seal destroyed | Shaft alignment and drive (universal joints that are not constant velocity, high radial load), inlet pressure against catalog values, a suction vacuum strong enough to turn the seal lip inside out, a dirty environment eating the lip. |
| Seal only leaking | Front shaft alignment and radial load, a lip cut during installation, inlet pressure over or under catalog values at any point in the machine cycle, a seal hardened by heat, acidic oil, and a seal that is too stiff for the job (a high pressure seal cannot follow a slight misalignment). |
The seal class is the last digit before any modification code in the model number. On Parker's T6C key sheet, 1 is S1 Buna-N (0.7 bar maximum, for mineral oil), 4 is S4 EPDM (7 bar maximum, for fire resistant fluids) and 5 is S5 Viton (7 bar maximum, for mineral oil and fire resistant fluids). When you replace the shaft seal, Parker says to use a protection cone over the shaft, and if you pulled the shaft without one, fit a new seal. Before you fit another one, read hydraulic pump leaking from the shaft.
What is the difference between a Denison T6 and a T7?
Both are fixed displacement vane pumps built around a drop-in cartridge, using Denison's hydraulically balanced design with pinned, double-lip vanes. The T6 family uses C, D and E size cartridges; the T7 family uses B, D and E sizes; a T67 is a multiple pump that mixes 6 and 7 series cartridges in one housing (a T67CB, for example, carries a C size 6 series cartridge and a B size 7 series cartridge). What the factory documents say differs:
| Point | What Denison documents |
|---|---|
| Cartridge sizes and displacement (T7, T67, T6C catalog) | B: 0.35 to 3.05 cu in/rev. C: 0.66 to 6.10. D: 2.68 to 9.64. E: 8.07 to 16.40. |
| Maximum pressure (same catalog) | B: 4,650 psi (4,350 psi in multiple pumps). C: 4,000 psi. D: 4,060 psi (3,500 psi in multiple pumps). E: 3,500 psi. Ratings drop on fire resistant fluids; check the table for your cam ring. |
| Rotation | The catalog lists B and D cartridges as bi-directional and C and E cartridges as uni-directional. The service kit list matches: industrial T6C, T6D, T6E and T7E use separate clockwise and counterclockwise port plates, while T7B and T7D use one bi-directional port plate. Mobile T6CM uses a bi-directional plate; mobile D plates are bi-directional as standard and uni-directional on high-speed builds. |
| Interchange (service and conversion kit list, 2005) | B and C size cartridges interchange in the same housing position (for example T6CC and T67CB). Complete D cartridges interchange between 6 and 7 series in the same position (T67DB and T7DB), but D cartridge parts do not. E cartridges and E cartridge parts interchange between 6 and 7 series. |
| Shared shaft and seal parts | The kit list puts the T6D and T7DS on the same shaft assemblies and seal kit (S24-10138), and the T6E and T7ES on the same seal kit (S24-10186). The T6C takes S24-10133 and the T7BS S24-49112. |
The practical upshot: do not order T6D cartridge parts for a T7D or the other way round, even though a complete D cartridge drops in. Order by the full model code.
How do I identify the cartridge in my Denison vane pump?
From the nameplate. A single pump code reads series, cam ring code (which sets displacement), shaft type, rotation, porting, design letter and seal class, for example T6C-B22-1R00-C1. Double and triple pumps carry one cam ring code per section. Cartridges are listed in the factory kit tables by cam ring code and by rotation, so you need both. Our Denison T6, T67 and T7 vane pump decoder takes the code field by field and gives the shaft part number for your series; the Denison pump model code decoder covers the wider range. If the tag is gone, see how to identify a pump with no tag.
Factory service sheets we host: T6C and T6CM service information, T7D and T7DS service (HY29-0074), plus the rest on our Denison vane pumps page.
Can I change the rotation of a Denison T6 or T7 vane pump?
Yes, and Parker documents it in section 3.3 of the T7, T67 and T6 overall instructions (HY29-0035). Whether it is a simple job depends on the port plates. With bi-rotational port plates the existing parts are reassembled the other way. With uni-rotational port plates you have to change the port plates to the other hand, which on a T6C, T6D, T6E or T7E means a pressure plate and a rear plate assembly, or a complete cartridge of the opposite rotation.
Read this first. Parker's instructions say modifications, conversions and repairs should only be done by authorized dealers or the OEM, or the factory guarantee may be invalidated. Never work on the pump with the drive running or the system under pressure. And remember the drive: the pump rotation has to match the electric motor or engine, viewed from the pump shaft end.
The procedure, rewritten from Parker's illustrated steps:
- Pull the cartridge. With the pump on the bench, remove the four main bolts, lift off the housing and draw the cartridge and front cap out with an extractor. A seal sometimes stays behind in the housing.
- Check which port plates you have. Parker's drawings show the bi-rotational plate with a choice of dowel pin holes and an arrow by each; the arrow nearest the dowel pin gives the rotation. A uni-rotational plate is made for one rotation only. If yours are uni-rotational, stop here and get the opposite-hand plates.
- Open the cartridge. Remove the two retaining screws and lift off the rear port plate. Depending on the position, the rear plate may or may not carry a bushing, and parts can stick to it.
- Flip the cam ring. Push all the vanes down into the rotor so they are not damaged, take the cam ring out and turn it over around its horizontal axis.
- Move the dowel pin from hole A to hole B, then seat the cam ring on it.
- Close the cartridge loosely. Refit the port plate and the two screws, but only snug them. Turn the rotor and vanes by hand to prove they run free, and line the pieces up as a true cylinder. Parker warns that a cartridge assembled out of concentric will not fit the housing.
- Reassemble the pump and torque the four main bolts: 187 Nm (138 lb-ft) on the T7B, T6D, T7D, T6E and T7E families, 159 Nm (117 lb-ft) on the T6C and T6CR. If the shaft came out without a protection cone over it, fit a new shaft seal.
- Re-mark and start up properly. Change the rotation letter on your records so the next person is not misled, then fill, bleed and start it like a new pump.
Rotation in general, and which other brands reverse in the field, is covered in hydraulic pump rotation: how to tell it and how to change it. Start-up after any rebuild or conversion: hydraulic pump start-up procedure.
Why won't my Denison Gold Cup pump stroke?
The Gold Cup is a different animal: an axial piston pump with its own integral servo and replenishing pump, and the stroke is moved by servo pressure. Denison's P6, P7 and P8 service manual (LT3-00058-2) gives replenishing pressure as 200 psi (14 bar) and servo pressure as 335 to 535 psi (23 to 37 bar). Its troubleshooting chart has no line called "no stroke," but the entries that cause one are there:
- Servo pressure too low to hold firm control. Denison's remedy is to raise the pressure and check the pressure drop through the servo filter. On the P6, P7 and P8 that is the servo strainer in the valve block. Read replenishing pressure at the KG gauge port before you condemn anything.
- Replenishing pilot valve set wrong. On assembly Denison sets it with about 1-1/2 threads showing below the small nut, which gives roughly 200 psi; each full clockwise turn adds about 50 psi.
- Eroded or worn parts in the displacement control, listed under mechanical faults that cause noise.
- Case not full. The manual says to fill the case before starting and keep it full, filling from the highest available point.
The same manual puts maximum case pressure at 75 psi continuous and 125 psi intermittent, never more than 25 psi above inlet pressure. See Parker Gold Cup piston pumps and our case drain flow test, which has the Gold Cup's allowable drain flow.
Frequently asked questions
Why is my Denison vane pump so loud?
Almost always air: aeration from a low oil level, a suction leak or returns above the oil, or cavitation from a starved inlet, cold thick oil, a clogged strainer or a pump mounted too high. Check alignment and the air bleed too. Parker's limit is never below 0.8 bar absolute (11.6 psia) at the inlet.
What is the difference between a Denison T6 and T7?
The T6 family uses C, D and E size cartridges, the T7 family uses B, D and E, and the T67 mixes 6 and 7 series cartridges. In the catalog, B and D cartridges are bi-directional and C and E are uni-directional. Complete D cartridges interchange between 6 and 7 series, but D cartridge parts do not.
Can you change the rotation on a Denison T6 or T7 pump?
Yes. Parker's HY29-0035 instructions show it: with bi-rotational port plates, pull the cartridge, flip the cam ring, move the dowel pin from A to B and reassemble. With uni-rotational port plates, such as the industrial T6C, T6D, T6E and T7E, you must change the port plates to the other hand.
Why won't my Denison vane pump prime?
Check rotation against the nameplate arrow, bleed air from the pressure line with the circuit unloaded, and check the inlet: gate valve open, oil level up, suction below the oil, no air leaks, and a vented tank. A fully sealed tank will not let it prime. Minimum speed is 600 rpm industrial and 400 rpm mobile.
Why does my Denison vane pump keep blowing shaft seals?
Usually inlet pressure or the drive. Standard seals are limited to 0.7 bar (10 psig) at the inlet, and a strong suction vacuum can turn the lip inside out. Misalignment, radial load from belts or unbalanced couplings, heat, acidic oil and lips cut during installation are Denison's other causes.
How do I tell which cartridge is in my Denison pump?
Read the model code on the nameplate: the series, the cam ring code for each section, the shaft code, the rotation letter and the seal class. Cartridges are listed by cam ring code and rotation, so you need both. Our Denison vane pump decoder walks through each field.
What servo pressure does a Denison Gold Cup need?
On the P6, P7 and P8, Denison lists servo pressure as 335 to 535 psi (23 to 37 bar) and replenishing pressure as 200 psi (14 bar). If servo pressure is low, the factory chart says to check the pressure drop through the servo filter.
About the technical information on this page. Figures, procedures and part numbers here come from manufacturer service literature and are provided for reference only. They are only as accurate as the factory data, and the revision we have on file may not be the latest for your unit. Always confirm against the current manufacturer documentation for your exact model and follow safe work practices. RestoPower is not responsible for damage, injury or loss resulting from the use or misuse of this information, or from incorrect assembly, adjustment, installation or operation of any unit.
Send us the full Denison model code
Give us the complete nameplate code, the symptom and what changed before it started. We will tell you whether it needs a seal kit, a cartridge, port plates for a rotation change or a rebuild, and we reply with price, availability and lead time. In-stock parts ship within 24-72 hours and in-stock parts carry a 2-year warranty. If the pump needs a rebuild, the teardown evaluation is free, you get a firm, itemized quote before any billable work, and the work is done in our shop or through the RestoPower repair network. Work done in our shop carries a 1-year repair warranty, and we arrange getting the unit to the shop doing the work.
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Related reading
- Denison T-series vane pumps and motors: parts catalog and rebuild guide
- Denison vane pumps and the Denison brand page
- Seal kits: Denison seal kits, shop Denison seal kits
- Denison vane pump model code decoder
- Hydraulic pump start-up procedure
- Hydraulic pump case drain flow test
- Hydraulic pump rotation: how to tell and change it
- Vickers vane pump cartridge kit rebuild
- Denison pump guide: Gold Cup, T6 and T7 series
- What a hydraulic pump repair costs