What pressure can a beersphere take?

[OliH]

Hello. I’ve been collecting free pressure barrels off market place. I’ve got 3 so far and, with a bit of love, all hold pressure.
I have
1 x youngs barrel with 2” cap rated at 15psi,
1 x Hambleton bard with a 4” cap
rated at 10psi.
1 x Beerspheer with red 4” cap pressure rating unknown?

Does anyone know the pressure rating for the beersphere?
I’m guessing 10psi, like the other hambleton bard, but hoped someone might know for sure.

Thanks in advance.