Inexpensive flow check valve?

[GasSavers_maximilian]

I need four flow check valves for my new heating system and am looking for a cheaper alternative (current ones are about $30 each). Swing checks are out because they don't have enough resistance to forward flow so you can get gravity driven heat circulation. I'd get pumps with integral ones, but I already have two pumps without. All the spring check valves I've found have too great an opening pressure to be useful with small centrifugal pumps. Anybody know a good source? I'm half tempted to add a light stainless steel spring to a swing check valve to increase its resistance to forward flow, but there's no way it'd be worth the effort. Thanks for any info.

Hmmm...maybe I could replace the spring on one of the spring check guys to make it open easier. That would be simple enough and I can get them for $7. Food for thought.

[GasSavers_Erik]

How about a swing check valve mounted in a vertical position or at a 45 degree angle (so gravity helps the flapper stay closed).

[GasSavers_maximilian]

That's an interesting idea, although my setup doesn't have the clearance for it. I guess I could try and rearrange things.

[GasSavers_maximilian]

Bought one of the expensive valves ($35, not $30) and it differs in several ways from the cheap valves I can get: high operating temp, manual override, moderate forward resistance, good, but not a perfect seal (no o-rings). Since I have multiple pumps, I don't care about manual override (allows gravity to provide some heat), I can get a higher operating temp (normally 190F) by replacing the delrin bearing with a bronze one and gettign a high temp o-ring (or just omitting it since the seal need not be great), and I can adjust the break pressure by trimming the spring (I can measure the pressure of the heating valve for a reference).

Of course I may be able to find the valve for less elsewhere, which would obviate this line of exploration, but since I can get four valves delivered for less than the cost of one of the expensive ones it's worth considering.

[GasSavers_maximilian]

Found the exact same valve for $20 on Ebay and they'll combine the shipping for not very much, so I'm just going that route.