Heidts valve (power steering) adjustment

[totem]

The pressure vs flow relation to level of assist is difficult to understand.

Looking at the Heidts valve patent, I understand it is a return type pressure limiting valve that is independant of flow. However, reducing pressure will reduce flow.

KRC pumps have swapable valve fitting with different flows.

Both are intended to adjust the level of assist but one works on pressure, the other on flow!

I might be wrong but I think that when there is no steering effort, oil flows in the system at zero pressure, keeping the pump cool. when effort is required pressure is build up to provide assist.

From that logic, I think lower pressure will lower the maximum level of assist but low flow will reduce the rate of assist.

But since there is still a pressure/flow relation, I cannot say which is best to improve steering feeling.

[2bking]

The pressure vs flow relation to level of assist is difficult to understand.

Looking at the Heidts valve patent, I understand it is a return type pressure limiting valve that is independant of flow. However, reducing pressure will reduce flow.

KRC pumps have swapable valve fitting with different flows.

Both are intended to adjust the level of assist but one works on pressure, the other on flow!

I might be wrong but I think that when there is no steering effort, oil flows in the system at zero pressure, keeping the pump cool. when effort is required pressure is build up to provide assist.

From that logic, I think lower pressure will lower the maximum level of assist but low flow will reduce the rate of assist.

But since there is still a pressure/flow relation, I cannot say which is best to improve steering feeling.

You are correct in the way you understand the principle of operation. It's the lines between the pump and reservoir that have the flow vs. pressure relation where it takes a certain pressure to deliver a certain flow so lowering the pressure certainly lowers the assist but also the volume of fluid available. The pump being a constant volume per revolution hydraulic device will put out that volume at any pressure until something breaks. Any pressure reducing device whether inside the pump or external has to reduce the volume to lower the pressure.

The problem occurs at high volume and pressure demands of the rack such as making a U turn and this is the only place I incurred the problem. I would get about a half a turn of the steering wheel with power assist and then it was suddenly all manual input needed to complete the turn. I first thought it was due to the belt slipping on the pump pulley and tighten the belt several times. Only when I dialed in more pressure to the rack did the problem go away. It could possible be a rack issue and not the pressure volume relationship.