Matbro TS270 relief valve constantly blowing.

ACEngineering is the guy to ask

Could be a steering priority valve problem but, as already said, @ACEngineering will have more idea...

Now Then.
Are you sure it's a relief problem?? The brake circuit will loose pressure over time, you should hear the engine note change as it recharges.
Years ago, I had one where it was drawing air into the suction hose from the tank. The boom services wouldn't work but a bit of steering got it going again.
There is a relief and a bypass valve in the 'In/Out' end of the main spool valve Assy which used to give trouble, but only lack of lift power..

DanniAgro said:

On my loader the relief valve keeps blowing if the controls are not used for a few minutes, but when you try to, say, raise the boom it does not respond until you move the steering wheel a few degrees. Then the relief stops blowing and the boom rises.
Is this a fault in the priority valve?

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You will hear the engine tone change regualar as and when it charges the brake accumulator which is normal.

Your problem is either within the steering priority valve, possibly a stuck spool or the brake charge valve screwed in to the steering valve is faulty or you have a major leak on the brake circuit dumping oil to tank, this will be caused by a worn out brake pedal valve and will meant the brake charge valve is constantly wanting to try and charge the brake circuit.

you can test the pedal by removing the hose on the back of the pedal valve, the top hose is return to tank so remove that and run the machine and no oil should be leaking out of the brake pedal.
(the bottom hose is the presure in and the hose on the front of pedal valve is the one going to the axles)

It could of cause be a worn out hydraulic pump thats so bad it cant get the brake pressure up enough to kick the brake charge valve off.

Matbro hydraulics are a pain in the arse, one problem often has multiple causes so ometimes the only way to fix them is chuck all the parts at it, often once one fails like the main relief valve on the spool block it ha a knock on effect on the rest of it and destorys the pump whihc then send metal everywhere and knackers the teering priority valve etc!

Worse case

Pump
Hydraulic tank clean and filters
main relief valve on the main spool block and reseal each slice.
steering priority valve comes complete with brake charge valve
brake pedal valve

DanniAgro said:

After removing the priority valve to have a gander, I can't see anything obviously wrong, apart from being unable to examine the interior of the brake charge valve as it's sealed by a welch plug.
Will get back to you after making further diggings in the hydraulics, but thanks for your suggestions ACEngineering and others.

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No being funny but you wont see anything wrong visually with the steering priorty valve, you can polish the spool rod up with wet and dry but that does not mean it wont stick under load, and as you say the brake charge valve has a core plug in the end of it covering the pre set pressure adjuster, you can unscrew it but then you will need a seal kit for it.
There is also another small core plug that hides the steering pressure relief valve but you only need to look at that if its leaking oil out the plug, can replace orings on that adjuster too.