VST relief valve assembly

[pstephens46]

Planning to clean/inspect VST this fall. How do you determine whether the relief valve assembly is working properly? Is it a check valve? Blow air through it both directions? Kinda expensive for a one way valve...

[rodbolt17]

it is a one way valve.
designed to break open and allow flow at about 10 psi.

[boscoe99]

Do you have a vacuum or pressure pump? Apply pressure or vacuum to the valve and let us know the reading at which it opens.

Regarding the expense, it carries the Yamaha brand.

Called a check valve in the SM. Called a relief valve in the parts book. It is Yamaha nomenclature.

[fairdeal]

[pstephens46]

Do you have a vacuum or pressure pump? Apply pressure or vacuum to the valve and let us know the reading at which it opens.

Regarding the expense, it carries the Yamaha brand.

Called a check valve in the SM. Called a relief valve in the parts book. It is Yamaha nomenclature.

Waiting for cooler weather. Prob late November after reds and trout slow up. But I will rig something and let you know. May need professor Fairwind to assist in laboratory preparation.

Headed up to Rodbolt's backyard to chase Tuna in a few weeks. Don't panic, I will not have time to visit Wanchese (spelling?)

[rodbolt17]

wunhceeze
it is at the end of the earth.

[pstephens46]

Do you have a vacuum or pressure pump? Apply pressure or vacuum to the valve and let us know the reading at which it opens.

Regarding the expense, it carries the Yamaha brand.

Called a check valve in the SM. Called a relief valve in the parts book. It is Yamaha nomenclature.

Thinking I might use the pcv valve off of a '79 Pinto.

[cpostis]

it is a one way valve.
designed to break open and allow flow at about 10 psi.

I may be way off base, but curious.

Is this the valve in the line from the VST pressure regulator to the Intake? When the motor is running, a vacuum is in the line and the valve opens providing operation on the regulator diaphragm to control fuel pressure(via relief/bypass)? Therefore there would never be flow through the valve? When not running, the valve would be closed?

Go ahead and tell me if I'm crazy, can you tell me operation otherwise if I am?

[rodbolt17]

ok
crazy

the valve in question is located between the VST inlet and the lift pump intake.

once the VST is full and the needle shuts off further fuel entry the relief valve opens and allows excess fuel to re-enter the lift pump intake.

remember at low speeds,below 1200 RPM, the lift pump cycles on 10 sec and off 20 seconds.
this helps prevent the lift pump from running in a semi stalled condition. it also aides in keeping the pump and fuel temps lower.

it also maintains about 10 psi on the vst inlet.

symptoms of the valve failing are typically stalling at low speeds after 10 min or so.

[boscoe99]

[cpostis]

ok
crazy

the valve in question is located between the VST inlet and the lift pump intake.

once the VST is full and the needle shuts off further fuel entry the relief valve opens and allows excess fuel to re-enter the lift pump intake.

remember at low speeds,below 1200 RPM, the lift pump cycles on 10 sec and off 20 seconds.
this helps prevent the lift pump from running in a semi stalled condition. it also aides in keeping the pump and fuel temps lower.

it also maintains about 10 psi on the vst inlet.

symptoms of the valve failing are typically stalling at low speeds after 10 min or so.

Thanks Rodbolt of KDH!
We"re talking about # 3 in the diagram below? I think I got it.

[cpostis]

OK Boscoe, but the diagram I posted is from pstephens F150txrd (the motor he's posted on before), what model diagram is the one you posted?

Which motor are we referring to Pstephens?

[boscoe99]

I am talking about the electric lift pump/VST pressure relief valve. I think Rodnut and fairdeal are talking about this valve also.

pstephens46 never told us the model for his motor. So, we are kinda shooting in the dark here. Only thing I really know about the OP's motor is that it is gray in colour. Or might be dark blue/black.

But a pressure relief valve is a pressure relief valve is a pressure relief valve. Unless it is not.

[cpostis]

I am talking about the electric lift pump/VST pressure relief valve. I think Rodnut and fairdeal are talking about this valve also.

pstephens46 never told us the model for his motor. So, we are kinda shooting in the dark here. Only thing I really know about the OP's motor is that it is gray in colour. Or might be dark blue/black.

But a pressure relief valve is a pressure relief valve is a pressure relief valve. Unless it is not.

Unless it's a check valve. Yamaha Ha, Ha, Ha!

[cpostis]

Oh by the way, In the diagram I posted, the check/relief "dual Yamaha" valve does not go to the pressure regulator. It does go to the top of the VST. Internally, I don't know what it does. Can anyone explain?

Don't get mad, I like to know how things work.

Thanks!!!